The Foreign Office has said it is urgently looking into reports that a British-Iranian man has been detained in Iran.
Abbas Edalat, a professor at London's Imperial College, was detained on 15 April while attending an academic workshop in Tehran, the Centre for Human Rights in Iran has said.
It claimed he protested his innocence and refused an offer of bail.
It is not known what charges - if any - he faces.
Mr Edalat's home in Iran was reportedly raided and his belongings confiscated.
The Centre for Human Rights in Iran, based in New York, described Mr Edalat as a British-Iranian national and anti-war activist who campaigns against foreign intervention in Iran.
It said he was detained by the Iranian Revolutionary Guard.
Imperial College has said it was also looking into the reports.
In recent years, Iran has detained several British-Iranian nationals, including Nazanin Zaghari Ratcliffe.
Mrs Zaghari-Ratcliffe, 39, is serving a five-year jail sentence after being convicted of spying charges.
Mrs Zaghari-Ratcliffe, who was arrested at Tehran Airport on 3 April 2016, has denied the charges against her.
The British-Iranian dual citizen maintains she was in Iran to introduce her three-year-old daughter Gabriella to her parents.
The BBC's diplomatic correspondent, James Landale, said the latest arrest comes amid growing tensions between Iran and the United States as the UK and other European powers try to stop both sides pulling out of the deal curbing Iran's nuclear capability.