"The Fed is making a mistake", he told reporters on Wednesday as he arrived in Pennsylvania for a campaign rally.
"I don't think there was any new news that came out of the Fed today that wasn't there beforehand", Mnuchin was quoted saying.
On Wednesday, he discounted the stock market's plunge - with the Dow Jones industrial average falling 831 points.
Trump has often pointed to stock market records set during his time in office as a measure of his success.
Trump has been publicly criticizing the Federal Reserve - led by Chairman Jerome Powell, whom he appointed - since July for interest-rate increases and declared he was "not happy" in September after the third rate hike of the year.
"I think it's good", Trump said of the stock decline.
Trump was briefed on the market turmoil earlier in the day, a White House official said.
O'Hare attributed the losses to worries about higher interest rates but also cited a "broad-scale deterioration in sentiment" as investors realized that the pullback on Wall Street failed to prompt bargain hunting to stabilize prices, as has been the norm in recent years. The problem I have is with the Fed.
President Donald Trump said the Federal Reserve is moving too fast with interest-rate increases and dismissed concerns about inflation, extending his run of criticism that central bankers have largely disregarded as they push ahead with higher borrowing costs.
Kevin Hassett, the head of Trump's Council of Economic Advisers, said the president is expressing his views on monetary policy, but he isn't trying to "politicize" the Fed.
The central bank's preferred measure of inflation is roughly at policy makers' 2 percent objective, and Powell said last week that "the outlook of forecasters inside and outside the Fed is for more of the same".
"The fundamentals and future of the USA economy remain incredibly strong", press secretary Sarah Sanders said in a statement after the close. Fed officials including Powell, Trump's handpicked chair, have said pointedly that they will not be influenced by comments from elected officials, and will make decisions based on economic data. "I like to stay uninvolved", Trump said.
During an event earlier Wednesday amid the sell-off, Trump and his top economic adviser, Larry Kudlow, said they believed the US economy was strong.
"The fundamentals and future of the USA economy remain incredibly strong", Sanders said in a statement.
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