In a letter of support (in Persian and English) to the family of the 94-year-old Nobel Peace Prize winner, the activists have expressed their best wishes for his health and full recovery.
"Mandela is the great human bring who reminds us of our dreams and wishes. We would like to pay our respect for him, especially for his long endurance of suffering and perseverance for the realization of common aspirations of humanity," the letter says.
It has been signed by prominent figures such as jailed human rights lawyer Nasrin Sotoudeh and award-winning film director Jafar Panahi, both of whom have come under pressure from the Islamic establishment.
Sotoudeh's husband posted a picture of the two dissidents signing the letter to Mandela's family on his Facebook page. Sotoudeh has signed the letter during her recent prison leave. Sotoudeh is serving a six-year jail sentence for security charges, including conspiring against state security.
Panahi is facing a six-year prison sentence and a 20-year ban on filmmaking.
The European Parliament awarded the 2012 Sakharov Prize for Freedom of Thought to Sotoudeh and Panahi, citing their courage in defending fundamental liberties in the face of oppression by the Iranian regime.