We explored this question in church on Sunday. Here is an excerpt from Sunday’s sermon on Choosing Sides:
A couple years ago a certain atheist web site presented what they called “The Blasphemy Challenge,” where they challenged people to upload YouTube videos of themselves denying the Holy Spirit. A whole lot of atheists responded to the challenge and uploaded their videos, saying “I deny the Holy Spirit.” It was very sad to see and meant to be shocking, but ironically enough, I am not sure they were actually blaspheming the Holy Spirit as Jesus defined it. They were certainly committing serious sin, but they were not attributing the work of the Holy Spirit in Jesus’ life to Satan.
In fact, I’m not sure if an atheist is even capable of blaspheming the Holy Spirit. If blasphemy of the Holy Spirit means believing that Jesus was doing supernatural works by the power of Satan rather than God, how can you do that when you don’t believe in the Holy Spirit, Satan or God?
What these atheists did is sad, it is wrong, and if they never come to Christ for forgiveness, they will be judged for their sin, but I do not believe they have actually put themselves beyond God’s forgiveness. By definition it would seem that an atheist cannot commit blasphemy against the Holy Spirit. (However, I would still recommend that you stay as far away from this sin as possible!)