Members of the Bank of Japan Policy Board raised concern about the side effects of adopting a negative interest rate at the central bank's January meeting, a summary of the minutes showed Monday.

Four of the board's nine members — Sayuri Shirai, Koji Ishida, Takehiro Sato and Takahide Kiuchi — opposed the step, according to a statement the BOJ released afterward.

At its meeting from Jan. 28 to 29, the BOJ decided to charge a negative interest rate of 0.1 percent on some of the accounts financial institutions keep at the bank.