The sit-in, third in a month, was organised by Human Rights and Peace Society and other rights groups against India's unofficial blockade and government's apathy towards addressing the humanitarian crisis created by the blockade.
Senior human rights activist Krishna Pahadi was among the 36 rights activists arrested by the police from Lazimpat, Kathmandu in front of the Indian Embassy gate as they were staging sit-in carrying placard which read "End blocakde, respect Nepal's sovereignty".
Madhesis are also protesting division of their ancestral homeland under the seven-province structure and have led an ongoing blockade of key border trade points with India.
At least 50 people have been killed in the protests since August.
The government has last month announced to amend the new Constitution to address two key demands of agitating Madhesis regarding proportional representation and constituency delimitation and tabled an amendment proposal in the parliament.