Tattep Ruangprapaikitseree of the Free Youth Group and his partner Panumas Singprom were arrested at their residence in Nonthaburi province on the outskirts of Bangkok and taken to a police station.
"We got arrested with many charges, but the most severe one is article 116," Tattep told reporters, referring to the sedition law.
He was seen flashing a three-finger salute, a symbol of the movement, when he arrived at police station.
The two were among 15 people charged in connection with a July 18 rally for breaching internal security laws and defying an emergency decree, which banned public gatherings to prevent the spread of the coronavirus.