AUD/USD was trading at 0.7100.
In testimony to Congress on Wednesday, Fed Chair Janet Yellen said conditions in the U.S. would allow it to pursue "gradual" adjustments to monetary policy.
Yellen said the US economy faces a number of global threats that could derail growth and compel the Fed to slow the pace of future interest rate hikes.
While the Fed expects to raise interest rates gradually, it is not on any pre-set course, Yellen said, adding that the central bank would likely move slower "if the economy were to disappoint".
Investors were eyeing Yellen's second day of testimony scheduled on Thursday.
NZD/USD edged down 0.18% to 0.6672.
Markets were also jittery as oil prices fell to a three-week low below $28 a barrel on Thursday.
The U.S. dollar index, which measures the greenback's strength against a trade-weighted basket of six major currencies, was steady at a four-month low of 95.77.