Steve Ballmer sees how investors 'could be a little worried' about a stock bubble

• "Are we in a market bubble or not? I don't know. I'm silent on it," former Microsoft CEO Steve Ballmer says.
• But investors "could be a little worried," he tells CNBC.

Former Microsoft CEO Steve Ballmer said Friday he can see why investors could be worried the stock market is in a bubble.

"Are we in a market bubble or not? I don't know. I'm silent on it. Where multiples are, etc., you could be a little worried," Ballmer said on CNBC's "Squawk Box."

"I killed myself in the late '90s when I said the stock market was overdone and we got a hiccup down the next day," he said.

Since the election, as of Thursday's close, the Dow Jones industrial average has surged more than 17 percent, the has gained 14 percent and the Nasdaq composite has risen 20 percent.

When asked whether President Donald Trump's pro-business policies have contributed to the market's gains, he said: "I have no idea."