Basically they cannot worship openly, since them believing jesus is the son of god is counter islam.
And there are less than half a million christians...
"The major part (89%) of the population in Iran is Shi'a Muslim, 10% is Sunni Muslim, and the remaining 1% are Christian, Zoroastrian, Baha’i and Jewish. Judaism has a very long history in the country, although the Revolution and the establishment of Israel have left just under 9,000 Jews in the country. Christians are the largest minority religion at 250,000 to 370,000. Most Christians have an Armenian origin."
