A number of Iranian servers and websites - including those of some petrochemical firms - were under a cyber-attack, said reports on social media.
There was no immediate official comment, and the websites of the main state oil company NIOC appeared to be functioning normally, said Reuters.
Residents said their internet access was not affected.
NetBlocks, an organization that monitors internet connectivity, said its data showed "intermittent disruptions" to some internet services in Iran starting on Friday evening.
But the group said the impact was limited, affecting only specific providers, and the cause was unclear.
"Data are consistent with a cyber-attack or unplanned technical incident on affected networks as opposed to a purposeful withdrawal or shutdown incident," it said in a tweet.
NetBlocks Director Alp Toker said they saw four Iranian networks falling offline over a three hour period on Friday evening.
This began when the first reports emerged and ended shortly later, Toker said. The networks have been stable since.
He said the affected networks were all relatively small and only one is a consumer service provider, so there was no massive nationwide impact. But it is notable that these networks are usually stable, he said.
