Tom Peterffy, billionaire founder of Interactive Brokers, told CNBC on Thursday that he may soon change his bearish tune about the stock market.

Peterffy, who turned negative on stocks in June, said right now his firm's customers have more than $50 billion of idle cash in their accounts, calling it a historic high.

"That enormous pile of cash is there waiting to come into the [equities] market," Peterffy said on "Squawk Alley."

Stocks seesawed in the red in volatile trading Thursday, a day after the Dow Jones Industrial Average plunged nearly 832 points, or 3.15 percent. The recent rapid rise in bond yields has been weighing on equities, adding to concerns about future Federal Reserve monetary policy. On Thursday, Treasury yields fell from multiyear highs after weaker-than-expected inflation data.

The central bank has raised its benchmark interest rate three times already this year, most recently at the end of September. The Fed, which meets two more times this year, is expected to hike rates one more time.

Peterffy believes the stock market can coexist with rising rates.

However, he's waiting to see what happens in the midterm elections next month, when he expects a "blue wave."

Democrats getting an edge in Washington will make China more willing to make a deal on trade because it will look like President Donald Trump has a weaker hand, argued Peterffy, whose Interactive Brokers has more than $6 billion in equity capital. "Give me post-midterm and give me another 2 to 3 percent down and I think the market will turn. So, I would not worry."

— CNBC's Fred Imbert contributed to this report.

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