There is even talk of witnessing a Christian revival, especially among young people living in the country, say Open Doors ministry workers in the Middle East.
A house church movement within Iran is part of that revival and has triggered "many secret meetings". The growth in the number of Christians is reportedly happening in all regions, but mostly in larger cities.
Iran is ranked 5th on the Open Doors 2012 World Watch List of the top 50 worst persecutors of Christians.
"Open Doors workers think that the growth of Christianity has everything to do with Iranians getting to know the real face of Islam, the official religion of Iran, and the mistrust of the people toward the government and leaders following the fraudulent 2009 presidential election of Mahmoud Ahmadinejad," said a Middle East worker for Open Doors, whose name has been withheld for security reasons.
There have been ongoing reports of the arrest and detention of Christians by the Iranian authorities.
In one city alone, Isfahan, more than a dozen Christians were arrested in less than a month, beginning in late February.
According to Open Doors USA President and CEO Carl Moeller, a stream of Christianity has arisen in the Middle East's invisible church, sometimes referred to as the Muslim Background Believer Church.
"Men and women, out of emptiness of their current situation spiritually, are turning to faith in Jesus Christ despite the literally lethal risks in doing so," Moeller said. "That's only attributable to the work of the Holy Spirit."
Also, at work is a common personality trait of the Iranian people, says another Open Doors worker from the Middle East region.
"Iranians are very outgoing and want to speak about their faith," the ministry worker said. "That is why discipleship training (with elements of outreach and communications) for Iranian believers is successful. If you tell them that a Christian should share, the Iranian Christian shares."
An estimated 200 Muslim Background Believers (MBBs) were living in Iran 40 years ago, according to Open Doors. Now, the number of MBBs is estimated to be 370,000.
Iran also has the presence of the traditional Armenian and Assyrian church with about 80,000 members, Open Doors reports. These churches are presently free to have meetings in the language of their members, but they are not allowed to reach out to the Farsi-speaking Muslims.
According to the Iranian government, there are about 200,000 Christians living in Iran, Open Doors stated.