At least four gunmen have reportedly intruded into the premises of the Majlis, opening fire on the security guards there, PressTV reported.
According to Tasnim news agency, at least eight people have been injured in the shooting attack on Wednesday.
A security guard is said to have lost his life in the firefight.
The assault has forced a lockdown on the legislature.
Tehran MP Elias Hazrati has said that the assailants were armed with two Kalashnikovs and a handgun.
According to lawmaker Mehdi Kiaee, the situation is under control inside the parliament, while security forces are working to restore calm there
ISNA quoted an MP as saying that all the parliament doors are shut and one of the assailants has been surrounded by security guards.
Separately, the Fars news agency said in a Twitter post that three gunmen attacked the Imam Khomeini Mausoleum in Tehran, opening fire on people inside and wounding a number of them.
The report said one of the assailants has been killed, another has blown himself up and a third one has been injured.
Informed sources say a suicide bomber’s explosive vest has also been discovered and deactivated in the vicinity of the mausoleum.