Rajab-Ali Mazroui, who is also a reformist former MP, had his passport confiscated, the news agency said.
He had been due to to take part in a meeting of the International Federation of Journalists, “so this decision will have repercussions around the world,” association spokesman Masoud Houshmand Razavi said.
In a letter to judiciary chief Ayatollah Mahmoud Hashemi Shahroudi, Mazroui protested the travel ban, stressing: “No court has prohibited me from leaving the country.”
No explanation was immediately available from the judiciary.
An outspoken champion of press freedom, Mazroui was prevented from defending his seat in parliamentary elections last year, after being blacklisted by the conservative-controlled Guardians Council, which vets candidates for public office.
Last autumn, the judiciary detained his son, Hanif, for his work on reformist websites.
Mazroui has campaigned vigorously on behalf of his son and scores of other journalists and technicians held for their internet work. They were eventually released but only after several had been required to publicly recant and ask the authorities for forgiveness.
Nobel Peace laureate Shirin Ebadi meanwhile announced that she would defend a reformist journalist who has been barred from covering the Iranian parliament for allegedly being “rude” to MPs in the conservative-controlled assembly.
Massih (Masoumeh) Alinejad, lobby correspondent of the reformist daily Hambasteghi (Solidarity) and the Iranian Labour News Agency (ILNA), insists the real reason for her ban is her exposure of the large year-end bonuses MPs awarded themselves last month.
“Publishing the amount deputies receive as a bonus is not an offence,” Ebadi said.
“This is why I decided to defend this journalist in the name of the freedom of expression,” she told Tehran newspapers.
The issue is a sensitive one as the conservatives took control of parliament last year on a promise to end what they said was wasteful spending of public money on MPs’ salaries.
MPs voted themselves an 11 million rial (1,200 dollar) annual bonus, many times more than the 168 dollars awarded to civil servants.
