Sense of agency (SoA) refers to the feeling that we are in control of our actions and, through them, of events in the outside world. One influential view claims that the SoA depends on retrospectively matching the expected and actual outcomes of action. However, recent studies have revealed an additional, prospective component to SoA, driven by action selection processes. We used event-related potentials (ERPs) to clarify the neural mechanisms underlying prospective agency. Subliminal priming was used to manipulate the fluency of selecting a left or right hand action in response to a supraliminal target. These actions were followed by one of several coloured circles, after a variable delay. Participants then rated their degree of control over this visual outcome. Incompatible priming impaired action selection, and reduced sense of agency over action outcomes, relative to compatible priming. More negative ERPs immediately after the action, linked to post-decisional action monitoring, were associated with reduced agency ratings over action outcomes. Additionally, feedback-related negativity evoked by the outcome was also associated with reduced agency ratings. These ERP components may reflect brain processes underlying prospective and retrospective components of sense of agency respectively.