According to the anti-persecution charity Christian Solidarity Worldwide (CSW), two men were sentenced in June 2013 for security-related charges.
Bijan Farokhpour Haghighi and Eskandar Rezaie have now been recalled from bail to serve prison sentences.
Mr Haghighi was sentenced to three years in prison, and Mr Rezaie was sentenced to one year, respectively.
Sources close to Christian Solidarity Worldwide (CSW) state that Eskandar Rezaie has been imprisoned at Adelabad Prison, while Bijan Farokhpour Haghighi is likely to be imprisoned soon.
The men were part of a group that was arrested when security forces raided a prayer meeting in October 2012.
In July 2013, the group was charged with 'action against national security' and 'propaganda against the order of the system'.
The men appealed, however the sentences were upheld in a decision issued in March 2014.
At the time of their arrest, the National Council of the Church of Iran said, "In accordance with the Gospel, the Church is apolitical.
"While individual Christians are entitled to hold political opinions, the Church does not.
"These charges are entirely without foundation.
"However, as loyal citizens we will continue to pray for our leaders and for peace and reconciliation in our nation."
CSW's Chief Executive Mervyn Thomas said: "It is both disappointing and deplorable that the Iranian regime persists in sentencing and imprisoning religious minorities on security-related charges.
"These Christians do not constitute a threat to the state and we call for their unconditional release.
"We urge the government to end the practice of characterising legitimate religious activities as national security crimes, and to uphold the right of all religious minorities to freedom of religion or belief, as articulated in Article 18 of the International Covenant on Civil and Political Rights (ICCPR), to which Iran is a signatory."
Listen to Premier's Hannah Tooley speak to the spokesperson for the Middle East and North Africa, here: