Cryptocurrencies, especially bitcoin, have become popular recently in part because of their sharp rise in prices. In 2017, bitcoin rose from less than $1,000 to more than $20,000 in some exchanges.
Still, Buffett sees them as largely speculative assets. "It's buying something because you expect the pool of people who want to buy it because they want to sell it to somebody else will grow," he said.
Bitcoin traded around $9,000 on Monday, well off last year's highs.
Buffett also compared buying bitcoin to investing in gold. "If you go back to the time of Christ, and you look at how many hours we had to give up in order to buy an ounce of gold and you bring it forward to now, you'll find the compound rate may be a tenth or two-tenths of 1 percent, … but it doesn't produce anything."
— Buffett joins "Squawk Box" for three hours, 6 a.m. ET to 9 a.m. ET, with special guests Munger and Microsoft co-founder and philanthropist Bill Gates.
With Berkshire's 2018 annual meeting in the books, users can revisit the highlights in CNBC's Warren Buffett Archive, which houses searchable video from 25 full annual meetings, going back to 1994, synchronized to 2600 pages of transcripts. The Warren Buffett Archive also includes 500 shorter-form videos arranged by topic, CNBC interviews, a Buffett Timeline, and a Berkshire Portfolio Tracker.