Warren Buffett said he's not at all discouraged that the stock market is under pressure due to the conflict in Ukraine.

In a live interview Monday on CNBC's "Squawk Box," Buffett said, "When I got up this morning, I actually looked at a stock on the computer (for) the trades in London (of a stock) that we're buying, and it's down and I felt good." He would only acknowledge it is an "English" stock.

"We were buying it on Friday, but it's cheaper this morning and that's good news." Will he buy more? "Absolutely."

Buffett said that would be true even if he knew Ukraine would turn into a major conflict.

"You're going to invest your money in something over time. The one thing you can be quite sure of is if we went into some kind of very major war, the value of money would go down. That's happened in virtually every war I'm aware of. The last thing you'd want to do is hold money during a war. You might want to own a farm, you might want to own an apartment house, you might want to own securities. During World War II the stock market advanced."

Buffett recalled that he bought his first stock in 1942, just after Pearl Harbor, when the macro situation didn't look very good, either.

Buffett also rejected the idea the U.S. stock market is "rigged." He said he doesn't think of the stock market as a market at all. To him, it represents "American business." He contended that the market's sheer size gives him comfort, "It's pretty hard to rig 20 trillion-plus dollars."

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Echoing a theme from his letter to Berkshire Hathaway shareholders released Saturday, Buffett said nonprofessionals don't need to be experts to do well with stocks. He recommends they buy a Vanguard S&P 500 stock index fund, which mirrors the overall market's performance.

An index fund keeps costs low, which Buffett said is tremendously important when investing, because fees act like a tax on returns.

(Download the complete CNBC transcript here.)

Buffett said that in his will he recommends that 90 percent of the money for his wife should go into an index fund. Why not Berkshire stock? "That would be fine, too," he replied, but he doesn't like "touting" it.

Buffett: Keystone is 'good idea' for country

Buffett said if it were up to him he would vote "yes" to approve the controversial Keystone pipeline even though it could take some business away from Berkshire Hathaway's rail subsidiary, BNSF.

"It's not that big a competitor. I think probably that the Keystone pipeline is good for the country." He has "no idea," however, if President Barack Obama will approve it.

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Buffett said the shale oil boom has helped BNSF. He acknowledged, however, that rail cars carrying the oil will need to be made safer and promised they will be.

"The oil from the Bakken, and from the Eagle Ford as well, turned out to be more volatile than people anticipated. ... We've lowered the speeds. It's going to require another kind of tank car, too."

BNSF announced previosuly that it will be buying 5,000 new tank cars. "We have found in the last year or so that it's more dangerous to move certain types of crude certainly than was thought previously."

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In late December a North Dakota town had to be evacuated after a BNSF train carrying Bakken crude derailed and caught fire.

Buffett: Bitcoin 'isn't a currency'

In response to a question, Buffett said bitcoin "isn't a currency" and he "wouldn't be surprised" if it's not around in 10 or 20 years. Since the price keeps moving around so dramatically, "it's very speculative, a Buck Rogers kind of thing" like the Dutch tulip mania in 1637.

Buffett on IBM and Heinz

Buffett conceded he knows less about major Berkshire holding IBM than he knows about Wells Fargo, one of his banking favorites. He knows enough, however, to feel comfortable about owning the stock and IBM's move lower means "nothing" to him. He conceded that IBM's revenue trends have been below expectations, but he likes the company's stock buybacks. He also endorsed CEO Ginny Rometty. "I feel fine with her, but her record will be judged five years form now. There's a lot going on in that business."

Buffett said he expects Berkshire will keep Heinz, its 2013 acquisition, "forever," although there could be an initial public offering. He thinks Heinz will be a profitable, worldwide business for a long time.

He didn't appear to be too concerned that some McDonald's restaurants stopped serving Heinz ketchup because co-owner 3G also owns Burger King. He expects Berkshire will have similar minor conflicts as it gets bigger in the future.

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On the economy, Buffett said the moderate but consistent growth that started in 2009 is continuing. That's reflected in the performance of Berkshire's businesses, although bad weather is "certainly" a factor.

Buffett wouldn't split Pepsi

Responding to a viewer's question, Buffett said he doesn't think PepsiCo should be split up, as investor Nelson Peltz has been advocating. He thinks the Frito-Lay business is an "extremely good," better than the soft drink business. "But I think the soft drink business is good, too, and I don't see any reason to split them up."

He believes activist investors are generally looking to turn a quick profit. There's nothing wrong with that, but he thinks it's better to build shareholder value over the long run by building earning power over time.

Buffett said Coca-Cola, a major Berkshire holding, is "under a lot more pressure than it was 10 or 15 years ago, especially in the United States." But, he said, Coke's sales go up every year and it has "wonderful" brands and acceptance around the world. "I drink five a day and I'm feeling good."

Berkshire 'too big to fail?'

Buffett said, however, that "it's very unlikely" Berkshire Hathaway will be designated by the government as a "too big to fail" firm. He said the designation of systemic importance to the financial system is "not based on size, it's based on whether you're likely to get in trouble." Buffett has heard "absolutely nothing" from the government on the matter.

On the debate in Washington over raising the minimum wage, Buffett said it "cuts both ways" and he could "argue either side of that." He does think it makes sense to increase the earned income tax credit to help the working poor. It's "the better way" because you can accomplish "way more" without the negative, and hard to quantify, effects of raising the minimum wage.

—By CNBC's Alex Crippen. Follow him on Twitter @alexcrippen