"If the yen rises or falls suddenly, then this will have an impact on the economy," Finance Minister Taro Aso said.
"Considering that the dollar was around 79 yen when our government started, it would not be a mistake to say it has fallen rapidly."
Against the yen, which has come under pressure after the BOJ's jolt last week, the dollar traded at 115.23 yen. It surged to a seven-year high of 115.42 yen on Thursday.
The BOJ is buying up government bonds and riskier assets to push down yields and meet a 2 percent inflation target sometime in the fiscal year starting in April.
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Inflation has picked up since the BOJ launched its quantitative easing program last year, but the decline in yields has also caused the yen to weaken steadily.
Japan is trying to distance itself from 15 years of debilitating deflation, and a weak yen does help because it makes imports more expensive.
Many policymakers also counted on a surge in exports as the yen weakened. However, export volumes remained flat as many companies have shifted production overseas.
Aso said a weak yen is still a positive because it improves exporters' earnings, but many small companies and households are starting to worry that the rise in import costs is wiping out the benefits of increased profits.
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"As cabinet minister, I can't say what currency levels are desirable," said Economics Minister Akira Amari.
"Whether it's excessive yen rises or yen declines, currency moves hurt the economy when they are too rapid. It's desirable for exchange rates to stabilize at levels that reflect Japan's economic fundamentals."