The dynamic mechanical behavior of poly(aryl ether ether ketone) (PEEK) films submitted to various treatments, i.e. physical aging, crystallization, and immersion in various solvents (water and some alcohols), has been investigated at low temperatures in order to give new insights on the origin of the subglass transitions. Two processes, i.e., the simple thermorheological component at lower temperatures and the cooperative component at higher temperatures, are overlapped in the beta relaxation of dry PEEK. Sorbtion of such solvent molecules as water, ethanol, methanol, and isopropanol gives rise to new relaxations.