You cannot hold public office or testify as a witness if you do not believe in God.

The Law

Article 19, Section 1 of the Arkansas Constitution explicitly states that no person who denies the being of a God shall hold any office in the civil departments of the state. It also bars atheists from being competent to testify as witnesses in any court. Though rendered totally unenforceable by the U.S. Supreme Court, this 1874 provision has never been formally amended out of the state's constitution.