It is always better to align our mind with universal peace and happiness. Then everything will coincide only with this ultimate thought about peace and happiness. Whoever reads, he can only read universal truth.
Evil thoughts are harmul to own self..... irrespective of whether anyone or God can read your mind or not, your own knowledge of your evil thoughts would be enough for their harmful effects to take place.
Eric is right. It is generally accepted that we have privileged access to our own mental states. However, assuming that God exists, in the traditional conception of God, he would be able to read your mind yes. He'll convict you of thought crime. Celestial North Korea.
I don't think anyone can read the thoughts except God. A human being is a combination of several spirits. A human being is just a toy to these spirits. All our knowledge and feelings are spirits (not one). A thought is a spirit. Another thought is another spirit. The thoughts regarding the thoughts of our past is another spirit. When we analyze these thoughts many spirits take part in the mission. I think God deals with only these spirits or one of these spirits and not with human beings directly. But I don't think God has work with human beings because He had finished everything with the spirits. The judges, advocates, saviors and all are spirits.