By Agence France-Presse
The benchmark Nikkei 225 index lost 1.33 percent or 300.89 points to close at 22,396.99, while the broader Topix index was down 0.36 percent or 6.28 points at 1,738.70.
The dollar dropped on Friday after Trump tweeted that Beijing and the EU were "manipulating their currencies and interest rates lower" to gain a trade advantage.
The dollar remained weaker in Asia, changing hands at 110.97 yen against 111.55 yen in New York late Friday.
"The current level of the yen is not in a zone that is concerning," said Hikaru Sato, senior technical analyst at Daiwa Securities.
"But the market remains nervous as no one can predict if Trump will make more remarks on currencies," Sato told AFP.
Investors were also awaiting Japanese corporate earnings reports beginning this week.
"If companies such as Nidec, Fanuc and Tokyo Electron post sound profits, the Nikkei index could rise above the 23,000 level" this week, said Tsuyoshi Nomaguchi, strategist at Daiwa Securities.
Gaming giant Nintendo dropped 2.54 percent to 36,370 yen, chip-making equipment manufacturer Tokyo Electron was down 0.58 percent at 18,645 yen, and industrial robots maker Fanuc plunged 2.33 percent to 20,660 yen.
Sony lost 0.75 percent to 5,888 yen with Toyota down 1.73 percent at 7,311 yen.
On Wall Street Friday, the Dow added 0.3 percent to close at 25,199.36.