Mohammadi, who has long campaigned against the use of the death penalty in Iran, had before her latest arrest been working with families seeking justice for loved ones who they say were killed by security forces in the 2019 protests.
Even while out of prison, she had in May 2021 been handed a sentence of 80 lashes and 30 months in jail on charges of "propaganda" against Iran's Islamic system.
Activists have decried what they see as increased repression in Iran over the last months, including the jailing of campaigners and greater use of the death penalty.
Prominent detainees have also died in prison, such as the well-known poet Baktash Abtin.
Another top rights defender serving a lengthy sentence in Iran is prize-winning lawyer Nasrin Sotoudeh who defended women arrested for protesting against the requirement for Iranian women to wear the hijab.
While she is currently believed to be out of jail on medical leave, supporters fear she is at risk of being imminently returned to prison.