The Nikkei 225 index edged down 2.88 points, or 0.03 percent, to 9,705.91.
Traders welcomed a report by payrolls firm ADP showing US companies added 201,000 jobs in March, the third straight month when more than 200,000 jobs have been created, raising hopes for government data due Friday.
Optimism in the strength of the US economy was boosted by remarks from three senior Federal Reserve officials who suggested the bank could bring an early end to its bond-buying programme, known as quantitative easing.
The improving outlook sent the dollar higher. The greenback fetched 82.90 yen in early Asian trade, up from 82.88 late in New York on Wednesday.
The Japanese currency was also pressured by talk of an interest rate hike by the European Central Bank, which saw the euro jump to 117.25 yen from 116.81 on Wednesday.
However, dealers remained cautious as workers battled to avert a catastrophe at the Fukushima Daiichi plant that was rocked by the March 11 quake and tsunami amid reports of radiation leakage around the complex.
TEPCO, which operates the plant, gained 8.6 percent at to 506 yen after the utility suffered a huge sell-off since the crisis began.
Nissan Motor rose one percent to 738 yen following a Nikkei report that the auto maker is considering setting up a holding company with France's Renault SA, although Nissan has denied any such plans for now.