They were produced before the Chief Judicial Magistrate Imphal East who remanded them to 15 days judicial custody, a report from the court said.
Kamei and Stephen have been in judicial custody in Imphal Central Jail since January after Manipur police arrested them on November 25 last for leading the indefinite blockade.
Representatives of the Manipur government and agitating UNC had gone to New Delhi to take part in tripartite talks called by the Centre on February 3 for a solution to the three-month indefinite economic blockade by UNC in the state.
The economic blockade has led to extreme shortage of essential commodities including food items, life-saving drugs and motor fuel.
Indian Oil Corporation had airlifted diesel to Manipur to mitigate the impact of the fuel crisis triggered by the blockade.