From the New York Times’s website:

Update | 1:50 p.m. Since our last post, the number of journalists reported to have been arrested since the June 12 election has risen to at least 24. Newsweek reporter Maziar Bahari was arrested without charge on Sunday morning in Tehran, and has not been heard from since, the magazine announced Sunday. Mr. Bahari, a Canadian citizen, has been living in and covering Iran for the past decade. His most recent article for Newsweek examined opposition supporters’ concerns that pro-Ahmadinejad groups were staging violent incidents at their rallies to undermine support for their movement.
Update | 1:13 p.m. The Paris-based media advocacy organization Reporters Without Borders is tracking the press clampdown in Iran and reports that 23 journalists have been arrested since the disputed June 12 election.
The group posted a day-by-day accounting of the arrests on its Web site on Sunday:
Among those arrested on Saturday, according to the report, was Ali Mazroui, the head of the Association of Iranian Journalists. The online news daily Roozonline.com reported last week that security forces had broken into Mr. Mazroui’s house and said they were carrying arrest warrants for his son Hanif Mazrui, a journalist and blogger.
Even prior to the disputed vote, Iran had routinely jailed popular bloggers, notably Hossein Derakhshan, an Iranian-Canadian blogger who was arrested last November and charged with spying for Israel.