Yes, once you're truly saved it's impossible for you to lose your salvation. Check out these verses:

(1 John 2:19 NIV) They went out from us, but they did not really belong to us. For if they had belonged to us, they would have remained with us; but their going showed that none of them belonged to us.

(Ephesians 4:30 NIV) And do not grieve the Holy Spirit of God, with whom you were sealed for the day of redemption.