Past interventions haven taken place during periods of low liquidity, allowing the authorities to move prices more sharply, or, as analysts put it, get the most "bang for their buck".
In such cases, the Ministry of Finance decides when to step in and the Bank of Japan acts as its agent.
The yen fell slightly on Monday in line with the broader market, and last stood at 156.62 per dollar.
It remained pinned near last week's 10-month trough of 157.90, though the yen appears to have found a floor after Finance Minister Satsuki Katayama ramped up verbal warnings of official yen buying on Friday.
Japan can actively intervene in the currency market to mitigate the negative economic impact of a weak yen, Takuji Aida, a private-sector member of a key government panel, said in a television programme on public broadcaster NHK on Sunday.