They were arrested from the south-eastern Nepali Siraha district on Saturday, and brought to Kathmandu for the filing of treason charges at a Special Court that looks after cases of treason and matters of national sensitivity.
According to the Alliance for Independent Madhes (AIM), among those charged were Sudipraj Kushwaha (26), who acted as the Election Officer, and Chandeshwar Mahato (60), who acted as international observer in the mock referendum held on December 26 in Siraha district. The third accused is Bishnudev Chaudhary, 35, a central member of the AIM.
The Alliance for Independent Madhes has been holding mock referendums for 'Free Madhes', as a form of peaceful protest, in the southern districts of Nepal.
In recent weeks, the government has intensified its brutal suppression against Madhesi activists through arbitrary arrests, torture and false charges, the alliance said adding that two other activists were arrested last year in November. They are still in jail.
The Nepal government has accused the alliance of hatching a conspiracy to split the country and said it is getting strong backing from C.R. Raut, a hardcore independent Madhes supporter.
Raut is advocating Swaraja, or self-governance, in Nepal's southern plains and has been holding a series of activities, protests and demonstrations. Raut once faced treason case but was released on bail later.
Nepal Police had also arrested over 100 'Free Madhes' activists in November from the Terai for launching the campaign.
AIM is a coalition of Madhesi people, activists, political parties and various social organisations working for the independence of Madhes, through non-violent and peaceful means following the principles of Gautam Buddha, Mahatma Gandhi and Nelson Mandela.
The alliance, that advocates "an end to Nepali colonisation, racism, slavery and discrimination" imposed on the Madhesis, stands for independent Madhes, democratic system, and peaceful and non-violent means.
Protests and demonstrations in Nepal's southern plains during the last more than four months have taken more than 55 lives and led to an embargo at key Nepal-India entry points.
"Acknowledging that the rights to freedom of speech, movement, peaceful assembly and association are the fundamental rights of all human beings everywhere, as also mandated by the United Nations Universal Declaration of Human Rights (UDHR) and International Covenant on Civil and Political Rights (ICCPR), of which Nepal is a signatory, we expect acknowledgement and assurance of the rights to freedom of expression, movement and peaceful assembly from the state and its agencies," the AIM said in a statement.