A two-dimensional (2D) numerical simulation is presented to study the effect of magnetic field on Ag-MgO nanofluid forced convection and heat transfer in a channel with active heaters and coolers. A Fortran code according to Lattice Boltzmann method (LBM) is developed for this purpose. The effects of thermal arrangement (Case1, 2 and 3), block side length (0.3 <= h <= 0.5), Reynolds number (50 <= Re <= 100), Hartmann number (0 <= Ha <= 60) and volume fraction of nanoparticles (0 <= phi <= 0.02) on flow pattern and heat transfer characteristics are analyzed systematically. The obtained results showed that the highest value of local Nusselt number occurs at the junction of the heater and the cooler due to the high temperature gradient, followed by the sharp corner of heaters and coolers. Moreover, the heat transfer at the heater sharp corner is higher than that of the cooler sharp corner. The average Nusselt numbers indicated that the rate of heat transfer increases with increasing phi or decreasing Ha. Finally, the heat transfer rate in Case 1 is more than Case 3 and Case 2. (C) 2019 Elsevier Ltd. All rights reserved.