Mojtaba Atarodi, 55, an assistant professor of electrical engineering at Iran's Sharif University of Technology, had been detained on suspicion of buying high-tech U.S. laboratory equipment, previous Iranian media reports said.
The trade sanctions were imposed over Iran's nuclear programme, which Iranian officials say is for peaceful energy purposes only but Washington says is secretly geared to developing the capability to produce nuclear weapons.
Iran's semi-official Mehr news agency said Atarodi arrived in Tehran on Saturday, after a stopover in Muscat on Friday.
Upon arriving at Tehran's Imam Khomeini airport on Saturday, Atarodi told reporters that he had tried to buy simple equipment for his personal lab to conduct academic research when he was detained by U.S. authorities, according to state-run Press TV.
There was no immediate U.S. comment on Atarodi's case.
Oman, a U.S.-allied Gulf Arab state which also enjoys good relations with Tehran, has previously helped mediate the release of Western prisoners held by the Islamic Republic.
Omani authorities had worked with U.S. officials to speed up Atarodi's case and return him home, the foreign ministry in Muscat said in a statement carried by local media.
He was released after follow-up approaches by Iran's foreign ministry, its spokesman Ramin Mehmanparast was quoted as saying by the Iranian Students' News Agency (ISNA).
In a report on its website dated January 7, 2012, Press TV said Atarodi was taken into custody on his arrival in Los Angeles on December 7, 2011, accused of buying advanced lab equipment.
Iran and the United States severed relations after the 1979 Islamic Revolution that overthrew the pro-Western monarchy in Tehran.
In 2011, Iran freed into Omani custody two U.S. citizens who had been sentenced to eight years in jail for spying.
Josh Fattal and Shane Bauer, among three people arrested while hiking along the Iraq-Iran border in 2009, were flown to Oman after officials there helped secure their release by posting bail of $1 million. They denied being spies.
The third detainee, Sarah Shourd, had been freed in September 2010, also by way of Oman.
(Reporting by Saleh al-Shaybani and Sami Aboudi; additional reporting by Zahra Hosseinian in Zurich and Yeganeh Torbati in Dubai; Editing by Mark Heinrich)
