The latest attack on Saturday was against Mar Girgis church in the town of Rafah bordering the Gaza Strip. There were no injuries or major damage.
The explosion comes amid nearly two weeks of civil unrest in the country as protesters continue to demand the resignation of President Hosni Mubarak, who has ruled for 30 years.
Christians, meanwhile, have been forced to gather in their homes for prayer, fearing for their safety if they meet at church.
At the start of the New Year, 23 Coptic Christians were killed and 80 were injured in a church bombing in Alexandria. The attack was condemned by church, human rights, and world leaders, including US President Barack Obama.
Christians, who make up eight to 12 per cent of the population, have been calling for greater protection from the state. Amid the ongoing protests, they are praying for a new Egypt, with democracy and freedom for the persecuted minority.
Mubarak announced on Tuesday that he will not seek re-election in September but anti-government protesters have indicated that they will not stop their demonstrations until Mubarak resigns.