Thanet Anantawong, a political activist, has sought political asylum abroad, Thai media reported on Sunday.
Mr Thanet, 25, was initially wanted on a lese majeste charge under Section 112 of the Criminal Code but the charge was later dropped. He is facing sedition charges for violating Section 116 of the Criminal Code.
He was among a group of student activists who attempted to visit Rajabhakti Park in Hua Hin early last month to hold a protest, but were intercepted by military officers.
They were on a train from Bangkok bound for Hua Hin when soldiers disconnected their carriage from the rest of the train at a railway station in Ratchaburi province.
Mr Thanet appeared in an interview with former television anchorman Jom Phetpradab in the Thai Voice programme broadcast on YouTube from an unknown country.
He said he had left Thailand to seek political asylum abroad. He did not name the country he was staying in.
After the military court issued the arrest warrant, Mr Thanet reported to the court and was freed on 100,000 baht bail under the condition that he must not take part in any political activity or incite unrest. He was to report to the court every 12 days.
Mr Thanet said he did not report to the court again because he was not at the core of the anti-government activists, just an ordinary democracy-loving citizen.
He said he believed the National Council for Peace and Order was trying to link the red-shirt protest in 2010, which he joined, to the current anti-NCPO movement.
He fled because power-holders in the country lacked justice. He would have stayed to fight if he had confidence in the justice system, Mr Thanet said.
"The military asked me to be its informant, to report on the activities of students moving against it. I could not do as requested. This is another reason I had to flee," Mr Thanet said.
Mr Thanet said he fled alone and nobody else went with him.