There was no indication the government would intervene in the currency market but it was keeping a close watch on the market.
"I think this is a move far removed from reality, and we will be troubled if this (trend) is underpinned," Finance Minister Yoshihiko Noda told reporters, Kyodo News reported.
A day earlier, Noda had called the yen rise "slightly one-sided."
Noda's comments came as the dollar dipped below 79 yen in early trading Thursday, even as the Japanese economy, already under deflationary pressures, continues to feel the economic impact of the devastation from the of the March 11 earthquake and tsunami.
The dollar came under pressure because of warnings of a review of U.S. government bonds by major credit rating agencies if the U.S. Congress fails to raise the debt ceiling by the Aug. 2 deadline.