If by Christian you infer the literal interpretation of the word, taken from the greek Christianos, which means "follower of Christ", then no, there could never be a Christian al Qaeda. The reason being that nobody can truly be a follower of Christ and slaughter men/women/children in the name of Jesus, as well as killing themselves in the process. Suicide and murder both break God's laws, and while those who follow God have in the past murdered, the bible is clear on how God will judge them for doing so. Taking a life is a sin, and is only allowed in very selective instances, terrorism isn't one of them.
Could there be those who claim to come in the name of Jesus, as they slaughter humans, yes, but they'll be liars.