The benchmark Nikkei 225 index edged up just 0.20 points to 22,517.03 in early trade, while the broader Topix index was down 0.11 percent or 1.95 points at 1,742.88.
Falls in Japanese shares come after world stock markets mostly climbed Friday despite rising trade tensions, with the Dow snapping an eight-session losing streak, closing up 0.5 percent at 24,580.89.
On Monday, the dollar fetched 109.85 yen against 109.98 yen in New York later Friday.
"Concerns over a trade war have been weighing on the Japanese market, but we don't think the impact is grave enough to hit the US economy immediately," said Tsuyoshi Nomabuchi, a Daiwa Securities strategist.
"The biggest challenge for Japanese companies will be trade negotiations linked to the auto industry," he added.
"Falls in the Chinese market so far have had limited impact on the Japanese and US share prices, but this should be kept in mind as a potential risk."
In Tokyo, telecom giant SoftBank was down 1.14 percent to 8,301 yen and automaker Nissan was down 0.37 percent, while construction machinery giant Komatsu rose 1.76 percent to 3,167 yen and Hitachi gained 0.68 percent to 788.4 yen. (AFP)