Veera Somkhwamkid, former coordinator of the Thai Patriots Network, and Gen Boonlert Kaewprasit, known as Seh Ai, chairman of the Pitak Siam group, reported to the National Council for Peace and Order (NCPO) on Monday morning.
They were responding to an order announced on television last night for the two to report to the NCPO today between 10am-12am at the army auditorium in Bangkok.
They were accompanied by lawyer Nitithorn Lamlua.
The NCPO issued the summons after Gen Boonlert organised a reception party for Mr Veera at the Royal Turf Club. This was regarded as a political gathering held without NCPO approval.
Mr Veera was released on a royal pardon last week from a Cambodian prison where he served part of an eight-year jail sentence for espionage after crossing the border illegally.