The dollar had briefly gained earlier on Thursday as stocks slipped and after the European Central Bank disappointed some investors who had expected that it would expand bond purchases to junk bonds.
It was "a combination of weaker risk and short-term reaction to the ECB announcement that there would be no QE expansion," said Vassili Serebriakov, an FX strategist at UBS in New York.
The euro was last up 0.18% at $1.0883, the highest since April 16, after dropping to $1.0834 after the ECB meeting.
The dollar index against a basket of currencies fell 0.22% to 99.27.
The greenback has weakened from a more than three-year peak of 102.99 in late March as global central banks launched massive stimulus measures to protect economies from the coronavirus outbreak. The cross-currency basis swap for swapping yen LIBOR for dollar LIBOR turned negative on Thursday for the first time in a month, indicating strong overseas demand for dollars for month-end.