Speaking before a congressional committee, Yellen said the Fed's monetary policy must be carefully weighed.
If the US unemployment rate were to continue to drop and the larger economy were to takeoff, there is a risk rate hikes would need to be accelerated at a faster pace than markets would like.
"If we allow the economy to overheat, we could be faced with having to raise interest rates more rapidly than we would want, which could conceivably jeopardise that good state of affairs that we have come close to achieving," Yellen said.
Financial markets expect the next rate hike in December. The Fed last raised its benchmark interest rate in December 2015 from an unprecedented near-zero target - in place since the 2008 financial crisis - to a range of 0.25 to 0.5 per cent.
Yellen rejected suggestions made by Republican presidential candidate Donald Trump that the Fed was refraining from raising rates in order to aid Democrat Hillary Clinton's campaign for the White House.
Yellen also said she was unaware of any meetings between Fed member Lael Brainard and the Clinton campaign, as reported by various media outlets.
- DPA