"But I'm actually not a trader. In the long run, I believe in index funds. In the long run, I believe in what my boys and girls at Microsoft can do. I'm pretty excited for the long term," he said. "Since I'm not selling, we'll see."
"I don't know if we're in a bubble or not," Ballmer added in a "Squawk Alley" interview. "I would have told you stocks were expensive when Microsoft was [in] the $70s, and I would have been wrong. And I thank goodness I held onto my Microsoft shares. And in addition, I own a bunch of index funds."
The last time Microsoft shares were in the $70s was in mid-2017. Microsoft stock has rocketed 30 percent since then, while the S&P 500 has surged about 15 percent.
Ballmer, owner of the Los Angeles Clippers and founder of the data-driven government analysis website USAFacts, said President Donald Trump's State of the Union address on Tuesday night was lacking on actual hard number targets on where the White House sees the country going.
State of the Union speeches are "kind of like a quarterly earnings call; what did we do, what are our plans and what are our forecasts," Ballmer said. "We were light on forecasts. What exactly is the jobs target? What are the plans to get there? Where are jobs today? Just as an example, and this is not particularly about this president. It's a general point about where we are."
The way to measure success is "numerics," not just to tout the passing of laws, said Ballmer, who became CEO of Microsoft in 2000 and led the software giant during a rocky 14-year tenure.
Shares of Microsoft were around $55 when he took over for co-founder Bill Gates right before the 1990s dot-com bubble burst. The stock hit a low of $15 during the financial crisis in March 2009.
By the time Ballmer stepped down and Satya Nadella took over as CEO, Microsoft shares had recovered to around $37. But overall, the Ballmer years saw the stock lose more than 30 percent of its value, compared with the S&P 500 's 22 percent advance.
Under Nadella, shares of Microsoft have nearly tripled, outperforming the 58 percent return on the S&P over the same stretch. On Wednesday morning, Microsoft was trading slightly below Monday's all-time intraday high of $95.45 per share.
Shortly after retiring from Microsoft in 2014, Ballmer bought the NBA's Los Angeles Clippers for $2 billion. He launched USAFacts last year.