A prominent Thai human rights lawyer faces a prison term of up to 150 years if convicted on 10 counts of royal defamation, the legal watchdog Thai Lawyers for Human Rights says.
Prawet Prapanukul, 57, provided legal assistance to members of a political opposition group, the United Front for Democracy Against Dictatorship, and served as legal counsel in a high-profile royal insult case.
He was detained in a raid on his home by police and troops at the weekend.
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Prawet appeared in a Bangkok court on Wednesday and was charged with 10 counts of royal insult and three counts of breaking Section 116 of Thailand's criminal code, the equivalent of sedition.
It was not immediately clear what Prawet might have written or said that led to his arrest and charges.
A spokesman for the military government said he was unable to comment on the case.
The lawyers' group said Prawet was charged along with five others, who also faced charges under the royal insult law.
He is in pre-trial detention at a Bangkok remand prison after being held incommunicado at the 11th Army Circle base in Bangkok, a facility the military uses as a temporary prison.
