Investors hesitated to build up aggressive positions before key data from major economies such as US jobs numbers on Friday and China's manufacturing activity index on Thursday.
Most Asian financial markets will be closed on Thursday for the Labour Day holiday.
South Korea's won eased on dollar demand from local importers and as investors took profits on the best performing emerging Asian currency in April.
Some traders suspected the foreign exchange authorities of buying the dollar to stem the won's appreciation, but many traders doubted such intervention.
The Philippine peso slid as the country reported a wider budget deficit in March.
Malaysia's ringgit eased as investors cut bullish positions.
Spot yuan hit a 18-month low against the dollar after the central bank fixed its daily mid-point weaker and on increasing corporate dollar demand.
Still, most emerging Asian currencies were poised to record monthly gains.
In April, the won outperformed emerging Asian currencies with a 3.0 percent gain to the dollar. That was the largest monthly percentage gain since September.
Inflows into stocks and bonds, attracted by strong economic fundamentals, have supported the South Korean currency.
The Philippine peso rose 0.5 percent while the Thai baht has appreciated 0.3 percent.
Singapore's dollar was up 0.1 percent.
However, the yuan has lost 0.7 percent in April, and was set to suffer a fourth consecutive month of depreciation which have more than erased its 2013 gains.
The Indonesian rupiah has fallen 1.8 percent and the Indian rupee has dipped 0.7 percent as investors took profits on election uncertainties from the two best performing emerging Asian currencies so far this year.