He was picked up from Subhashipally area in Alipuarduar district, police said.
Mr Thapa was part of the GJM delegation that met Chief Minister Mamata Banerjee at the state secretariat on August 29 to discuss peace in Darjeeling hills which has been rocked by violence since June 12 this year.
Jalpaiguri Superintendent of Police Amitava Maity, however, did not elaborate why Thapa was arrested despite being part of the meeting convened by the State government last month.
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