Flash events, where high-temperature dynamics such as sintering and superplasticity of ceramics are significantly promoted with electric fields above thresholds, have been attracting the scientific and technological interests. Earlier studies have suggested the ionic diffusion during flash is accelerated by the crystal defects potentially induced by electric fields and/or currents. In this study, the mechanical responses of yttria-stabilized zirconia flashed by AC electric fields were investigated through sound velocity and nanoindentation measurements at ambient conditions in order to evaluate the defect-induced dynamics. The observed anelastic behaviors (i.e., rate-dependent elastic softening) and their effects on high-temperature dynamics during flash will be discussed.