The deaths occurred after members of the Ali-Ilahi sect - who were armed with Kalashnikov assault rifles - attacked a police headquarters in the region of Mian-Doab near the city of Mahabad on Sunday.
The report, quoting provincial police spokesman Shahnam Rezaie, said several other people were injured.
On 29 September, police in the area were attacked by the group in an incident that left three members of the sect and one policeman dead.
News reports said two senior local police officials died in clashes in the same area the previous week.
The Ali-Ilahi (roughly translated as "Ali is my God") group has been described as "heretical" by Shia religious authorities.
Imam Ali is considered by Shia Muslims to have been the first successor of the Prophet Muhammad and their first imam, or spiritual leader, but the sect sees him as an incarnation of God.
A local official also said the apparent leader of the sect, identified as Said Agha Nazem, was posing as the 12th Shia Imam, Mahdi, who is known to the Shia as the "hidden imam".
Iran's spiritual centre is the city
of Qum in the south
The Shia believe Mahdi became the "hidden imam" after he disappeared in the year 873 CE.
Shia Muslims believe Imam Mahdi will one day return and usher in a period of justice and peace.
In recent months, followers of the Ali-Ilahi group have held small protests in Tehran and in the central Shia clerical capital of Qum.