This paper considers the problem of viscous dissipation effects on non-Darcy natural convection over a vertical flat plate embedded in a fluid-saturated porous medium. Forchheimer extension is considered in the flow equations and its contribution to viscous dissipation is considered in the energy equation. The nondimensional governing equations are solved, numerically, by the finite-element method (FEM). The resulting nonlinear integral equations are linearized and solved using Newton-Raphson iterations. Numerical results for the details of the stream function, velocity and temperature contours, and profiles as well as heat transfer rates in terms of the Nusselt number, are presented in graphs.