He was jailed for eight years in September 2012, following a government crackdown on the church gatherings he led.
However there are growing concerns his sentence will be extended after suggestions he may face new charges.
According to Middle East Concern, a family member was able to visit him this week and were told intelligence officers had interrogated him using a taser gun.
The new charges are linked to claims that he has connections with anti-government groups and has made statements and taken actions against the government. Pastor Saeed denies these allegations.
In a letter to supporters, the Christian charity call on believers to pray for Pastor Saeed. It says: "[Pray] that no new charges will be brought against Saeed, but that he will receive the medical care he needs and will be released soon. For Saeed's wife Naghmeh, their two children and the wider family.
"[Pray]that Saeed and all other prisoners in Iran will be treated with respect and dignity as beings created in the image of God and that others currently detained in Iran for their Christian faith or activities will be released and all charges against them will be dropped."
This weekend marks three years since his imprisonment. Prayer vigils are expected to take place around the world.