The Free Narges Coalition said in a statement that Mohammadi must be granted a medical furlough to receive comprehensive treatment for multiple conditions.
It said that just transferring her to the hospital won't address the severe health issues caused by months of neglect and deprivation.
Mohammadi is being held at Iran's notorious Evin Prison, which houses political prisoners and those with Western ties.
She already had been serving a 30-month sentence, to which 15 more months were added in January.
On Saturday, Iranian authorities issued an additional six-month sentence against her after she protested the execution of another political prisoner in the women's ward of Evin Prison on August 6.
Mohammadi suffers from heart disease, and according to her medical report issued in September, the main artery of her heart has again developed a serious complication.
The coalition said that they continue to demand the unconditional release of Mohammadi and her full access to medical care.
Mohammadi is the 19th woman to win the Nobel Peace Prize and the second Iranian woman after human rights activist Shirin Ebadi in 2003.
Mohammadi, 52, has kept up her activism despite numerous arrests by Iranian authorities and years behind bars.
