Economic recovery may take time, depending on progress fighting the coronavirus pandemic, he said.
The US Dollar Currency Index, which measures the greenback's strength against six major currencies, was little changed on the day at 100.02. The index slipped as low as 99.57 during the session.
"Powell clearly shelved the prospect of negative rates for now," Karl Schamotta, chief market strategist at Cambridge Global Payments in Toronto.
The dollar index has traded in a tight range over the past few weeks but remains just 3% shy of a more than three-year high hit in late March, supported by heightened demand for safe havens as financial markets remain on edge about the economic impact of the pandemic.
Elsewhere, the British pound gave up earlier gains to trade 0.2% lower on the day as bond yields fell after data showed the economy contracted by a record 5.8% in March even though household consumption dropped less than feared by some market participants.
The New Zealand dollar slid 1.0% after the country's central bank doubled the amount of bonds it was buying and opened the door to negative interest rates, sending long-term bond yields to all-time lows.