The benchmark Nikkei 225 index was down 0.69 percent, or 207.50 points, at 29,973.71 in early trade, while the broader Topix index slipped 0.60 percent, or 12.45 points, to 2,067.16
The benchmark Nikkei 225 index gained 0.52 percent, or 142.01 points, to 27,665.20 at the open, while the broader Topix index advanced 0.36 percent, or 6.92 points, to 1,931.90
A disappointing showing by Japanese Prime Minister Yoshihide Suga's Liberal Democratic Party (LDP) in a local election on Sunday added to the cautious mood
Drugmakers advanced, with the two leading percentage gainers in the Nikkei - Astellas Pharma jumping 3.69% and Chugai Pharmaceutical climbing 1.75%. Daiichi Sankyo rose 1.09%.
Elsewhere, the Australian and New Zealand dollars eased slightly as the Antipodeans struggled to break through heavy technical resistance, but sentiment remains positive due to rising commodity prices, some traders said.
Under a policy dubbed yield curve control, the BOJ targets short-term interest rates at -0.1% and the 10-year bond yield around 0%. It also buys risky assets such as exchange-traded funds (ETF) as part of efforts to fire up inflation.
8 US gross domestic product data is due later on Thursday to gauge the strength of the world's largest economy as it struggles with the coronavirus pandemic.
In Tokyo, Sony was down 1.03 percent at 10,605 yen, trading house Mitsubishi Corp was down 1.29 percent at 2,594 yen, and real estate firm Mitsui Fudosan was off 1.02 percent at 3,895 yen.