Finance Minister Yoshihiko Noda expressed concern after the dollar briefly fell below 76 yen last Friday.
"I am concerned that the one-sided strengthening of the yen has been accelerating," Noda told reporters. "We will not rule out any measures and will take tough action when proved necessary."
Kyodo News reported the minister said his government and the central bank, Bank of Japan, will continue to closely watch the market to assess "whether there are more speculative bets [on the yen's advance] than before."
The yen has continued to appreciate against the greenback despite a similar intervention on Aug. 4 that required the central bank to sell yen and purchase U.S. dollars.
The yen appreciation has been blamed on concerns over the economic situation both in Europe and the United States. A higher yen would make Japanese exports more expensive, further adversely affecting the country's economic recovery after the catastrophic March 11 earthquake and tsunami.