Current oscillation will occur when a piezoelectric ceramic vibrator is driven by a high electric field. The mechanism of current oscillation is discussed, based on the results of the present experiment. Ring-shaped lead zirconate titanate (PZT) piezoelectric vibrators are driven by a 5.65 V electric field with a fixed frequency of slightly less than resonance, to form an oscillating current. The sample current, temperature, and phase between the driven electric field and sample current are recorded. The resonance frequency of PZT rings shifts in the direction of low frequency under a high electric field due to the heat produced by dissipated power, and then shifts back due to the effects of aging, which results in current oscillation. The oscillation phenomenon is explained according to the production of strong internal stresses due to abrupt change in temperature, and then, aging process through the rearrangement of domains to relieve various stresses.