The country is being ruled by a military junta that staged a coup in 2014.
Ekachai Hongkangkwan was arrested on Saturday morning at his home in Bangkok, according to a statement by Thai Lawyers for Human Rights, Efe news reported.
Arrest warrants were also issued by the Southern Bangkok Criminal Court for another three activists who were involved in the protest, the statement added.
The group is charged with organising a gathering less than 150 metres from a royal site.
The protest was held to call for democratic elections after the junta had announced they would be delayed until February 2019, despite earlier assurances that polls would take place in November this year.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
