A computational study is presented of the enhancement of pressure recovery in a three-dimensional diffuser by using plasma actuators, as experimentally investigated by Grundmann et al., Exper. Fluids 50, (1), 217–231 (2011). The flow configuration utilizes a streamwise-oriented arrangement of dielectric barrier discharge (DBD) plasma actuators mounted on the top wall of the inflow duct. Spanwise motion directed towards the duct corners was generated, modifying the inflow with locally intensified turbulence. The most advantageous enhancement was achieved using an actuator pulsed with 40 % duty cycle. For comparison an actuator operating continuously (100 % duty cycle) was also considered. The present computational study examines both cases, comparing them to the baseline configuration with no actuation. Simulations were performed within the scale-adaptive version of the Unsteady RANS (Reynolds-Averaged Navier Stokes) framework by using an eddy-resolving second-moment closure as the turbulence model. The plasma actuator was represented using a spatial body-force distribution based on PIV (Particle Image Velocimetry) measurements of the flow induced by a plasma actuator, Kriegseis et al., J. ... mehrPhys. D: Appl. Phys. 48, 329401 (2015). The results obtained for both pressure-recovery enhancement and suppression correlate well with the experimental findings.