The Bank of Japan will look into a media report that said the BOJ board was discussing a negative interest rate policy just minutes before it surprised observers with the announcement.
"We'll start by examining the situation carefully, including the possibility that it was just based on speculation," said Tadaaki Kumagai, a spokesman for the BOJ. Kumagai would not comment further.
The report by the Nikkei news service came while Gov. Haruhiko Kuroda and the board were in the closing stages of a two-day policy meeting.