Christmas Day services will be held during the morning for safety reasons.
On October 31, militants laid siege to Baghdad's Our Lady of Salvation church, leaving 44 worshippers, two priests and seven security forces personnel dead in an attack claimed by Al-Qaeda affiliate the Islamic State of Iraq.
Ten days later attacks targeting the homes of Christians in Baghdad killed six people and wounded 33 others.
On Friday, Chaldean Catholic archbishop Monsignor Louis Sarko said in a message from Kirkuk that Iraqi Christians must remain steadfast, despite their fears.
"Today we are living a painful experience in Iraq, which reached its peak with the massacre at Our Lady of Salvation, which touched both Christians and Muslims. But we must persevere in the face of disaster," Sarko said.
"We will not surrender to division and frustration."
Father Saad Sirop Hanna, the priest of the Saint Joseph Chaldean Catholic church in central Baghdad, told his congregation at a Christmas Eve service: "Do not fear -- that is the message today."
"The Christian community this Christmas is very afraid, very scared of the situation, and we take seriously the threats that we've received by Internet or by emails," he said after the service.
In Saudi Arabia, Christians will be discreet in their celebrations, as the Gulf kingdom forbids the overt practice of any religion but Islam.
In the capital Riyadh, there are no signs of the Christmas season.
"We don't do much for Christmas; we have to be careful," said Raul, one of the more than one million mostly Christian Filipino workers in the country, who along with two other fellow welders from Pangasinan were shopping at the popular Pinoy supermarket in Riyadh.
"I put up some Christmas lights in my apartment, and made a tree in the shop," said Valentin, a metal shop worker from Cavite. "You can't buy a Christmas tree in Saudi Arabia."
Religious services take place, but are very hush-hush. The state oil giant Aramco, with thousands of non-Muslim employees, has long allowed services in its tightly guarded compounds in Eastern Province.
Although private worship in homes is protected under government orders, many Saudis including the religious police are unaware of that, and Christians are particularly cautious of attracting attention.
In other Gulf oil monarchies, major shopping centres have been particularly lively.
Various hotels in the United Arab Emirates have decorated trees, with one in Abu Dhabi housing a 13-metre-high (42-foot) version draped in jewellery said to be worth more than 11 million dollars (8.4 million euros), making it "the most expensive Christmas tree ever."
In shopping areas of the Syrian capital Damascus, Christmas ornaments, toys, Santa Claus suits and sweets can be found.
Christmas trees have also been raised in some Syrian cities, including one in Safita near Tartus in the east that is 18 metres (60 feet) tall and has 3,200 lights, with a large nativity scene nearby.
Lebanon, a tiny multi-confessional Mediterranean state that is the only Arab nation with a Christian head of state, is one of the few countries in the region where Christians enjoy full religious freedom.
Christmas celebrations there transcend the multitude of religious communities, members of which formed often sectarian-based militias in Lebanon's devastating 1975-1990 civil war.
Many Muslim families have Christmas trees and decorations, and gifts and Santa Claus are social phenomena in Lebanon's annual frenzy of buying that would match many Western states.
South of the border, crowds of tourists and Palestinians flocked on Friday into the West Bank town of Bethlehem, where Christians believe Jesus was born, to celebrate Christmas.