Yellen also defended the Fed's performance, saying it has not been too slow to raise the benchmark lending rates, given the tepid recovery and sluggish inflation.
The US central bank last raised the federal funds rate in December, only the second increase in a decade, but is widely expected to hike again at the March 14-15 policy meeting given the recent upward move in inflation.
The Fed's policy-setting rate committee "will evaluate whether employment and inflation are continuing to evolve in line with our expectations, in which case a further adjustment of the federal funds rate would likely be appropriate," Yellen said.
But she cautioned that monetary policy "cannot be and is not on a preset course."
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In the face of some critics, even among Fed officials, that the central bank risks allowing inflation to rekindle by raising rates so slowly, Yellen defended the committee's performance.
Waiting too long to raise rates could mean the Fed has to hike more rapidly at some point, which "could risk disrupting financial markets and pushing the economy into recession."
Still, she said, unless something worsens the economic outlook "the process of scaling back accommodation likely will not be as slow as it was in 2015 and 2016."
Many economists have pointed to the Fed's preferred measure of inflation, which recently reached a targeted two percent annual rate, but Yellen and other Fed officials have noted that higher energy prices are contributing to that increase.