Mixed convection in fully developed flows of air (Pr = 0.7) inside a channel subjected to oscillatory pressure gradients is studied numerically. The lower wall of the channel is periodically grooved to form square cavities, which are heated uniformly from the bottom. The following three pertinent parameters evolve as a result of the proper nondimensionalization of the governing equations: Re, the oscillatory flow Reynolds number (based on an oscillation velocity scale); Wo, the Womersley number; and Grq, a modified Grashof number. A low-Re range (10 < Re < 100), in which the flow properties are sensitive to small changes in Wo and / or Grq, is of primary interest in the present investigation. When the buoyancy effect is neglected, a circulatory roll cell appears inside the cavity, which remains over almost the entire cycle. However, the formation of such a vortex does not take place with the mixed convection mode; this difference stems from a deeper penetration of the throughflow to the cavity. Heal transfer enhancement at the heat flux surface prompts this structure change in the flow field as a manifestation of the buoyancy effects.