We must beware of false peace. Some who do wrong may have a peace about it, but it does not come from God. As someone has said, "Peace of heart alone is not always the peace of God."
A significant test to apply to determine the origin of the peace is this: If I have peace in my heart about a matter, do I also have peace with others in the Body of Christ concerning it?
Understandably, not everyone will agree on any single issue, but if only the person himself thinks he is right, he has reason to question his decision. If we are out of the will of God, we will bring discord and disharmony to the Body of true believers. I realize the difficulty in assessing who is a true believer, especially in a group situation. Sometimes those who are part of the group do not evidence salvation themselves.
Other times, some may clearly evidence salvation but give little evidence of mature judgment in things related to the Christian life. One of the best safeguards against a false peace is simply making sure that you have the desire to please Jesus Christ in all that you do.
If it is your concern "that in all things he might have the preeminence" (Col. 1:18), you can trust Him to bring conviction and a lack of peace when your life is not honoring to Him. "Great peace have they which love thy law: and nothing shall offend them" (Ps. 119:165).