The May surplus was up 58.1 percent from the same month of last year. In April, the surplus was up 100.8 percent year-on-year.
Current account is the broadest measure of Japan's trade with other nations and includes income from its foreign investments.
In its preliminary report, Japan's Finance Ministry said growth in direct investment income, or the country's earnings from its investments overseas, more than offset the trade deficit brought on by an increase in fossil fuel imports, Kyodo News reported.
The income account, spurred by higher dividends and profits from securities, recorded a surplus of 1,522.8 billion yen ($15.02 billion), up 8.6 percent year-on-year.
Japan's exports also have been rising due to a declining yen.