The purpose of this study was to determine whether the development of masseter muscle activity at mandibular rest position is characteristic for different angle classifications. The sample consisted of 64 boys and 108 girls, aged ten to 18. Electromyographic (EMG) activity from the right and left masseter muscles was recorded using an EMG scanner. First or second order polynomials were used to separately model the age-related changes in resting muscle activity of each gender and Angle's classification. The EMG activity of Class I boys and girls were expressed in positive second order polynomials. The EMG activities of Class II and Class III subjects were expressed in first order polynomials, and the EMG levels in Class III subjects were lower than in Class II subjects. These results indicated that development of resting activity levels might distinguish and characterize the anteroposterior mandibular position relative to craniofacial region.