The Foreign Ministry has revoked the passports of lese majeste opponent Somsak Jeamteerasakul and hardline red-shirt leader Wutthipong "Ko Tee" Kochthammakhun.
The passport revocation has been effective since Tuesday, ministry sources said.
The two men are believed to have fled abroad to evade arrest.
Mr Somsak, a law academic from Thammasat University, failed to report to the junta after being summoned by the coup-makers.
A warrant for his arrest was subsequently issued.
Mr Wutthipong is wanted on a lese majeste charge.