This work presents preliminary results of flow separation control from the flap of a high-lift airfoil using a single dielectric barrier discharge (DBD) plasma actuator. Control effectiveness is investigated for two actuator locations as well as various reduced frequencies, applied voltages and waveforms. Results show that a single DBD plasma actuator located at the flap shoulder can slightly increase or reduce the size of the time-averaged separation bubble over the flap depending on the frequency of actuation. This effectiveness is not improved by an increase in applied voltage or a change from a sinusoidal to positive sawtooth waveform for the cases examined. Spatial eigenmodes calculated from two-component PIV using POD show that a single DBD plasma actuator at the flap shoulder can have a significant effect on the structure of higher order modes. However the corresponding energy of these modes is low in comparison to the dominant modes in the wake.