Mixed convection flow and heat transfer characteristics in a lid-driven cavity with a circular body inside are studied numerically using a finite element formulation based on the Galerkin method of weighted residuals. Comparisons of streamlines, isotherms and average Nusselt number are presented to show the impact of the Richardson number, non-dimensional radius of the cylinder, and the location of the cylinder on the transport phenomena within the cavity. The results of this investigation show that the presence of the cylinder results in an increase in the average Nusselt number compared with a case with no cylinder. This result is observed for both, an adiabatic and isothermal, boundary condition imposed on the cylinder. The average Nusselt number increases with an increase in the Richardson number for all non-dimensional radius of the cylinder studied in this work. Moreover, the optimal heat transfer results are obtained when placing the cylinder near the bottom wall for various Richardson numbers. For dominant natural convection (Ri >= 2.5), the average Nusselt number increases with an increase in the non-dimensional radius for 0.05 < r(0)/H < 0.2. Further increase in the non-dimensional radius does not change the Nusselt number at a particular Ri. For dominant mixed convection, the average Nusselt number increases with an increase in the radius of the cylinder for various Richardson numbers. (C) 2013 Elsevier Ltd. All rights reserved.