"Their only crime was refusing to treat wounded men from Isis," Ismat Rajab, an official from the Kurdistan Democratic Party (KDP), told Rudaw.
Rajab added that the doctors were killed on Sunday, but did not disclose details of their identities.
Mosul, Iraq's second largest city, has been under the control of the Islamist group since June, with recent reports suggesting that elements of the civilian population have begun to turn against the militants and its brutal practices.
Isis has reportedly issued fatwas, or religious proclamations, forcing women to wear the Niqab or Burqa, banning the sale of cigarettes, alcohol, films and music and conscripting children to fight in its militias.
Rudaw also reports that Isis has seized six merchants, who refused to pay a monthly tax Isis has imposed, with their whereabouts currently unknown.
It is believed that Isis uses the tax to fund the military campaigns it is waging in Iraq and Syria.
In October, three women, two of whom were doctors, were executed by the militants in Mosul.
One female doctor spoke to al Akhbar newspaper in August of the climate of fear in hospitals, with doctors and nurses threatened, and female staff sexually harassed and raped.
"A so-called Abu Mo'men made a pass on me, even though he knew I was married with children," she said. "When I told my husband, he made some calls to people close to the militants, however, the situation turned against me because the next day Abu Mo'men threatened that he would cut my husband's head off if I do not keep quiet."
In July, the militants also killed a university professor, who criticised the group for forcing Christians to convert to Islam or pay a special tax.
The Wall Street Journal reports that locals have set up underground militias to combat the group, and provoke a local insurrection.