It is important to note that the default condition of the world is that of being under condemnation, according to John 3:18:
Whoever believes in him is not condemned, but whoever does not believe is condemned already, because he has not believed in the name of the only Son of God. John 3:18
All men have sinned and fallen short of the glory of God (Romans 3:23) and are already dead in their trespasses and sins (Colossians 2:13).
Consequently, the question is not so much if there is there any unforgivable sin that a Christian can commit that will result in his losing salvation. Rather, it is what an unbeliever does that precludes him from being made alive, forgiven, and given eternal life.
The answer is his failure to recognize Jesus as the Messiah and trust in His substitionary atonement on the Cross and His resurrection from the dead. The sin of the Pharisees was, when seeing the evidence of the Messiahship and Deity of Jesus, they rejected it.
We must understand that it is the Holy Spirit who "convicts the world of sin and righteousness and judgment" to draw them to faith. So, it seems that people can blaspheme the Father and the Son and be forgiven, yet blaspheming the Holy Spirit may result in the Holy Spirit ceasing to draw the person to faith in Christ, rendering that person unforgivable.
Forgiveness comes through faith in Christ, and faith in Christ comes at the beckoning of the Holy Spirit. So, once again, the blaspheming of the Holy Spirit may result in the cessation of His drawing of a person to faith in Christ.
And when he comes, he will convict the world concerning sin and righteousness and judgment: concerning sin, because they do not believe in me; concerning righteousness, because I go to the Father, and you will see me no longer; concerning judgment, because the ruler of this world is judged. John 16:8-11
So, yes, there is an unforgivable sin, but this isn't something a Christian can commit. It's something an unbeliever can commit by quenching the One who draws him to faith in Christ, through which forgiveness is received.