An independent commentator, Hasan Fathi, was detained by authorities in Tehran shortly after appearing on BBC Persian in a live broadcast on the Iranian ammunition depot explosion that killed at least 17 revolutionary guard soldiers on Saturday.
The arrest comes just weeks after the BBC described a "dramatic increase in anti-BBC rhetoric" and attempts to intimidate the corporation since it aired a documentary about Iran's supreme leader, Ayatollah Ali Khamenei.
The BBC said Iran had arrested friends and relatives of 10 members of staff and intensified blocking of its Persian channel, which is not authorised to operate in the country. The 10 people in question are now understood to have been released.
A BBC spokesman on Monday said that BBC Persian has "no correspondents or employees" in Iran, and that Fathi is just an independent commentator.
"The [BBC Persian] service spoke to Mr Hasan Fathi as an independent commentator, as it does to other independent journalists, academics and other public figures from Iran," the BBC said.
"We remain concerned about the ongoing efforts by the Iranian authorities to put pressure on the BBC for its balanced and impartial coverage, and to intimidate people who speak to us."
Jon Williams, the BBC's foreign editor, said on Twitter late on Sunday that the arrest was "very worrying".
Peter Horrocks, the BBC's head of global news, in October called on the UK government to rebuke Iran for its "widespread crackdown on freedom of expression".