U.S. equities closed mixed Thursday on the back of remarks made by newly minted Treasury Secretary Steve Mnuchin.

"Investors want to see more details," said Kate Warne, investment strategist at Edward Jones. "Investors are a little more cautious, but I wouldn't take this as a major shift" in market direction.

The Dow Jones industrial average rose about 35 points and notched its 10th straight record close, with Johnson & Johnson contributing the most gains. The S&P 500 closed marginally higher after reaching a new all-time high, with utilities rising more than 1 percent.

The Nasdaq composite underperformed, sliding 0.4 percent as the tech sector snapped a 15-day winning streak.

"You've got the economy improving on its own, even without tax reform," said Bruce Bittles, chief investment strategist at Baird. "I think we keep going higher until we get that. Then the market might top out."

In an interview with CNBC's "Squawk Box," Mnuchin said he wants to see "very significant" tax reform passed before Congress' August recess.

"We want to get this done by the August recess. We've been working closely with the leadership in the House and the Senate and we're looking at a combined plan," he said.

The prospect of tax reform has been one of the key catalysts in the U.S. stock market's postelection rally, along with deregulation and government spending.

