Mutation testing is a fault-based testing technique which provides strong quality assurance. Mutation testing has a very long history for the procedural programs at unit-level testing, but the research on mutation testing of object-oriented programs is still immature. Recently, class mutation operators are proposed to detect object-oriented specific faults. However, any analysis has not been conducted on the class mutation operators. In this paper, we evaluate the orthogonality of the class mutation operators by some experiment. The experimental results show the high possibility that each class mutation operator has fault-revealing power that is not achieved by other mutation operators, i.e. orthogonal. Also, the results show that the number of mutants from the class mutation operators is small so that the cost is not so high as procedural programs.