The believers spent four and a half years in jail because they belonged to unregistered Christian denominations.
Erin James from Open Doors, which supports persecuted Christians told Premier that despite the good news, the plight of Christians was still worrying.
Speaking during Premier's News Hour, she said: "It's great to see 35 Christians released from what is awful persecution in terrible and really extreme prisons and camps.
"However, we have to remember that there are over 300 Christians arrested last year and up to maybe 3,000 Christians in these prison camps altogether."
The Eritrean government only officially recognises the Orthodox Church of Eritrea, Sunni Islam, the Roman Catholic Church and the Evangelical Lutheran Church as religious groups in the East African country.
Most members of the released group are young and not church leaders. Prominent pastors and religious leaders are held in higher security prisons such as the notorious Karsheli prison in Asmara.
James told Premier the group's prolonged detention was unusual as they had all signed a document promising not to attend meetings of underground churches - following what's traditionally required from Christians belonging to unregistered denominations.
She added they hoped to be able to move abroad "and live out their faith".
"Do pray for these 35 as they adjust to life outside of prison. They've no doubt suffered immense trauma and torture so do be praying for them. Pray that they will be comforted.
"Pray for the government - this persecution is coming from the government... and just pray for Christians in general, especially the ones who are so scared they don't even let their neighbours know that they're Christians.
"Pray that they will have the strength to carry on, that they'll know that God is comforting them and that they can survive there."
There are an estimated 1,200-3,000 people detained on religious grounds across 60 prisons and camps that make up Eritrea's extensive prison network.
Eritrea is number four on the Open Doors World Watch List which ranks where Christians face the most persecution.
Listen to Erin James speaking with Premier's Tola Mbakwe:
Stay up to date with the latest news stories from a Christian perspective. Sign up to our daily newsletter and receive more stories like this straight to your inbox every morning.
