From a neurobiological and motivational perspective, the feedback-related negativity (FRN) and reward positivity (RewP) event-related potential (ERP) components should increase with reward magnitude (reward associated with valence (success/failure) feedback). To test this hypothesis, we recorded participants’ electroencephalograms while presenting them with potential monetary rewards ($0.00–$4.96) pre-trial for each trial of a reaction time task and presenting them with valence feedback post-trial. Averaged ERPs time-locked to valence feedback were extracted, and results revealed a valence by magnitude interaction for neural activity in the FRN/RewP time window. This interaction was driven by magnitude affecting RewP, but not FRN, amplitude. Moreover, single trial ERP analyses revealed a reliable correlation between magnitude and RewP, but not FRN, amplitude. Finally, P3b and late positive potential (LPP) amplitudes were affected by magnitude. Results partly support the neurobiological (dopamine) account of the FRN/RewP and suggest motivation affects feedback processing, as indicated by multiple ERP components.