You don't choose to believe or not believe anything. The belief is the outcome of a cognitive process. You can choose to expose yourself to certain information, but that doesn't guarantee what impression that information makes. You can listen to the 700 Club all day long and come away more opposed to its doctrines than you were before.
You could give false witness about God. Let's say that you have a personal encounter with God, and he says, "When you talk with Frank Biggleheim, tell him that you and I had a chat." And you believe this to be a real experience, not a dream or hallucination. When you talk with Frank, you say that God isn't real. What is blameworthy is that you are telling Frank something contrary to what you believe to be the truth. It's an action. However, this is not the position that nonbelievers are in. They honestly do not believe in God, and they aren't deliberately misleading anyone.
