A member of the Resistant Citizen group has been arrested on lese majeste and computer crime charges as the authorities' crackdown on dissidents continues.
Police on Saturday took Burin Intin to the military court, which approved an initial 12 days of detention while police gather more evidence. Suspects can be detained for seven 12-day periods before charges must be laid.
He might apply for bail early next week if lawyers from the Thai Lawyers for Human Rights Center can arrange a surety.
Col Burin Thongprapai of the National Council for Peace and Order (NCPO) said police had monitored Mr Burin's activities after they found him posting anti-government comments online.
On Wednesday, Mr Burin reportedly posted a 40-minute video clip titled "I want to be kidnapped" with the hashtag "Release our kidnapped friends".
That evening, Mr Burin joined a protest at the Victory Monument and was arrested along with 15 others and brought to the Phaya Thai police station.
The group held a "Stand Still" protest against the arrests in Bangkok and Khon Kaen of the "Facebook 8", the eight administrators of a Facebook page mocking Prime Minister Prayut Chan-o-cha. They were charged with breaking the 2007 Computer Crime Act and were denied bail.
Col Burin also said Mr Burin had committed lese majeste in his private chats with other people. Officers detained him on Thursday and sent him to computer crime police for further action.
Mr Burin denied he had destroyed evidence — a mobile phone he claimed he had given to a friend.
Police said no one had contacted them to hand over the phone.