An electric oscillating tool, having particular but not necessarily exclusive utility as an electric toothbrush, for driving a brush head assembly or end effector with a resonant mechanism at high frequencies. The electric toothbrush includes handle housing, an electromagnetic motor mounted in the housing, and a mechanical oscillator acted upon by the motor. One end of the mechanical oscillator extends outwardly through an opening in the handle housing while the other end is attached to the housing inside the chamber. The end effector/brush head assembly attaches to the extending end of the mechanical oscillator. A power source supplies an alternating current drive signal to the motor, in turn causing the armature and the mechanical oscillator to oscillate and drive the brush head assembly. Control circuitry senses the frequency of oscillation of the mechanical oscillator and controls the frequency of the drive signal to maintain the mechanical oscillator at resonance under the variety of loads imposed during use.