Last week, US stocks suffered one of the worst weekly falls in a decade, as an interest rate rise and US-China trade tensions rattled markets.
Mr Mnuchin said banks confirmed they had "ample liquidity" for operations.
It also comes amid a partial government shutdown over spending plans.
"The [bank's chief executives] confirmed that they have ample liquidity available for lending to consumer, business markets, and all other market operations," the Treasury said in a statement attached to a tweet from Mr Mnuchin.
"[Mr Mnuchin] also confirmed that they have not experienced any clearance or margin issues, and that the markets continue to function properly," the Treasury's statement said.
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