Christian Solidarity Worldwide (CSW) report that two of them, Mr Babak Hosseinzadeh and Mr Behnam Akhlagh, were arrested while attending church on Saturday 23rd February.
A third man, Mr Mehdi Khatibi, was arrested the same day, following a summons from the secret police.
The arrests bring the total number of Christians arrested in Rasht over the past five weeks to six peple.
Back in January, Hossein Kadivar (Elisha) and Khalil Dehghanpour were arrested.
On 10th February, Pastor Matthias Haghnejad was arrested by Islamic Revolutionary Guard members who entered the gathering where he was leading a service, detaining him after it had concluded.
Pastor Haghnejad has been arrested and tried on several occasions.
CSW's Chief Executive Mervyn Thomas said: "The arrests in Rasht are the latest in a heightened campaign of repression that has seen Christians receiving excessive charges and sentences merely for exercising their right to manifest their religion in private and in community with others and in a peaceable manner.
"Many more are being punished for adopting a religion of their choice in accordance with article 18 of the International Covenant on Civil and Political Rights, to which Iran is party.
"CSW urges the Iranian authorities to ensure the immediate and unconditional release of all who have been arrested or imprisoned unjustly. These arrests and sentences constitute a grave violation of the Iranian constitution, as well as of the nation's international legal obligations."
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