In written responses Thursday to questions from Representative Brad Sherman, Yellen said that "while I would not completely rule out the use of negative interest rates in some future very adverse scenario, policy makers would need to consider a wide range of issues before employing this tool in the United States, including the potential for unintended consequences."

Sherman submitted his queries following the Fed chief's Feb. 10 hearing before the House Financial Services Committee, of which he is a Democratic member. It comes at a time when the Fed is debating whether to raise interest rates, even as global economies including the euro area and Japan employ negative-rate policies to stoke economic growth and inflation.

"By some accounts, these policies appear to have provided additional policy accommodation," Yellen wrote. "We certainly are trying to learn as much as we can from the experience of other countries."