The five activists --Varavara Rao, Arun Ferreira, Vernon Gonsalves, Sudha Bharadwaj and Gautam Navlakha-- are under arrest at their respective homes since August 29.
Prominent people who signed the letter included economist Jean Dreze, Afzal Anees and Kavita Srivastava.
Arrest of activists ploy to divert attention from failures of BJP governments: Mayawati slams 'government terror'
The BSP chief said the government was trying to intimidate poets, lawyers, activists, human rights advocates, professors and intellectuals.
Bhima Koregaon violence: Three out of five arrested activists brought to Pune court, SC to hear plea challenging arrest
The three Left-wing activists were arrested yesterday by the Maharashtra Police and brought to Pune late last night.
The speeches at the conclave, held on December 31 last year to mark the 200th anniversary of the Koregaon-Bhima battle, had fuelled the violence a day later, they said.