The effects of Joule-heating, chemical reaction and thermal radiation on unsteady MHD natural convection from a heated vertical porous plate in a micropolar fluid are analyzed. The partial differential equations governing the flow and heat and mass transfer have been solved numerically using an implicit finite-difference scheme. The case corresponding to vanishing of the anti-symmetric part of the stress tensor that represents weak concentrations is considered. The numerical results are validated by favorable comparisons with previously published results. A parametric study of the governing parameters, namely the magnetic field parameter, suction/injection parameter, radiation parameter, chemical reaction parameter, vortex viscosity parameter and the Eckert number on the linear velocity, angular velocity, temperature and the concentration profiles as well as the skin friction coefficient, wall couple stress coefficient, Nusselt number and the Sherwood number is conducted. A selected set of numerical results is presented graphically and discussed.