The broad S&P 500 index closed sideways, the Dow Jones industrial index fell 0.1 percent, while Nasdaq's technology-heavy composite index closed 0.1 percent plus.
The Fed left its key interest rate in the range 4.25—4.50 percent, where it has been since December.
Fed chief Jerome Powell said during a press conference after the interest rate decision that "we are starting to see some effects" on inflation from President Donald Trump's tariffs, but that the central bank will be able to make better decisions regarding interest rate adjustments if they wait a few months.
Concerns about the situation in the Middle East pushed down stocks earlier in the week and pushed up oil prices. On Wednesday, Trump said that he "maybe" will draw the US into the war, "or maybe will not do it".
Both the investment bank Goldman Sachs and the major bank JP Morgan closed up 1.7 percent on Wednesday.
Even the electric car giant Tesla rose 1.8 percent. Other tech giants included in "The magnificent seven" - "the magnificent seven" moved more cautiously.
