Transmission electron microscopy (TEM) specimens of Zr-based metallic glasses were prepared from amorphous ribbons. Shear bands produced by bending these specimens were located by TEM. High resolution transmission electron microscopy analysis indicates the existence of nanoscale void-like defects and high-density areas in shear bands. The formation of these defects is believed resulting from the evolution of stress-activated free volumes during the mechanical loading and the removal of external stress, which can be understood by comparing the stress-induced processes in shear bands in analogy with the thermal annealing effects on similar metallic glasses