Elaheh Ansari and Reza Estiar are among dozens of Internet users who told The Associated Press that their access was back on Monday.
The semiofficial Mehr agency had said that more than 30 million people in the country were affected by the outage.
Authorities in Iran's national telecommunications company declined to comment, saying the outage had no connection to them.
Iran has occasionally restricted the Internet since the turmoil that followed the 2009 presidential elections and blocked websites including Facebook, Twitter, Voice of America and the BBC Farsi service.
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