Abstarct: In the present study, natural convection in a porous cavity is investigated numerically by finite volume method. It is assumed that a non-isothermal bioprocess occurs, which may lead to make internal heat generation in the cavity. The source term in the energy equation is proportional to the generation rate of solute concentration governed by a Monod model. It is assumed that the vertical walls are at constant temperatures and bottom wall and top wall is with the isothermal temperatures.This problem is concerned for both cases, that in the one case the porous cavity is assumed to be a non-homogenous with thermal equilibrium. In this case three-laxyer porous medium is considered inside the cavity to investigate the effects of porosity variation and there is an internal heat source in this cavity. The effects of variable porosity on heat transfer, biochemical heat source, flow pattern and mass transfer is investigated. The obtained results in the case of variable porosity are compared with those of constant porosity condition. In two case the porous cavity is assumed to be an homogenous with thermal non-equilibrium, that there is a internal heat source in the fluid phase. The influences of the non-dimensional parameters on the flow pattern, temperature distribution and mass transfer are also presented. The temperature distribution is shown for both solid and fluid phases at the mid-plane and center of the cavity. The Darcy model was used as momentum equations in the porous medium region. The fluid inside the cavity is assumed to be an incompressible, Newtonian and Boussinesq. The fluid flow is assumed to be two-dimensional, unsteady and laminar.