An extensive mechanical spectroscopy study in the low-frequency range is proposed to evidence and characterize the effect of a deformation below the glass transition temperature (T-g) on the mobility in an amorphous bisphenol-A polycarbonate. The mechanical treatment induces the appearance of a peak more than 100 K below T., which presents the characteristics of a relaxation associated to an unstable nature. This phenomenon is related to the creation of shear-induced high-mobility zones. The characteristics of these zones appear to be independent of the deformation level applied to the system. The use of a specific procedure allows the determination of the values of the apparent activation energy of the mechanism. The apparent activation energy increases continuously from the values of the beta-relaxation to the main alpha-relaxation ones. (C) 2008 Wiley Periodicals, Inc.