Senior Superintendent of Police Ajith Rohana said the two activists were produced before a Magistrate overnight and set free after being questioned by the police Terrorist investigations Division.
However, further investigations into Ruki Fernando and Catholic priest Father Praveen Maheshan will continue.
Fernando and Maheshan were arrested in the northern town of Kilinochchi over the weekend and were transferred to Colombo for investigations.
The arrest sparked an outcry that prompted the United States and Britain and human rights groups in Sri Lanka and overseas to demand for their release.
The incident was also raised at the United Nations Human Rights Council currently ongoing in Geneva, but the government defended the arrest saying it was linked to attempts by Tamil Tiger rebels to regroup in the North.
A woman from the north who was arrested earlier on similar charges remains in detention as investigations continue.
The government said Balendran Jeyakumari was arrested over allegations she harboured a Tamil Tiger suspect in her house. (BERNAMA)