"I can emphatically say that partisan politics plays no role in our decisions," Yellen told reporters after the Federal Open Market Committee's two-day policy meeting.
Trump, the Republican presidential nominee, recently suggested that the Fed kept interest rates low to help President Barack Obama's administration. Yellen said, "We do not discuss politics at our meetings, and we do not take politics into account in our decisions."
She highlighted the Fed's dual mandate to promote maximum employment and price stability, while stressing the central bank's role as an independent government agency.
The Fed's policymaking committee kept the federal funds rate unchanged at 0.25 to 0.50 percent, though 3 of the 10 voters supported a quarter-point hike. The Fed's statement indicated it could support a rate rise this year, saying "The case for an increase in the federal funds rate has strengthened," but that it would wait for more progress toward its objectives.
The policymaking committee's statement highlighted "solid" job gains but added that inflation is still running below its 2 percent target.