We recruited patients with orbitofrontal lesion (OFC; n = 18), right lateral prefrontal cortex lesion (LPFC; n = 9), and healthy age-matched controls (CTR; n = 22) to perform a self-paced, two-choice random generation task (adopted from Iwanaga & Nittono, 2010). We compared how each set of participants responded to the perceivable consequences of their voluntary actions while recording behavioral responses and electroencephalography (EEG). All participants repeatedly pressed both a left and a right button, but not at the same time. Each button was normatively associated with its own tone, a 1 kHz tone for right button presses and a 2 kHz tone for left button presses. Participants were instructed that their button presses should be random, in a measured manner, without overlap (roughly 1500 ms between presses), and that the tones that their button presses produced were task-irrelevant. After an initial 20 presses, a button press would occasionally produce the tone normatively associated with the other button (p = 0.132) and this condition was classified as a cognitive mismatch. The standard condition, when a button press produced its expected tone was classified as a cognitive match. Event-related potentials (ERPs) were extracted from the EEG recording in relation to these two conditions. In CTR participants cognitive mismatch trials elicited enhanced N1, N2, P3, and a late positive potential (LPP) components. The OFC group had an ERP that indicated they did not differentiate between instances of cognitive match and mismatch. The LPFC group had an ERP on cognitive mismatch trials that was not highly differentiated from cognitive match trials, except for a posterior P3a component. Comparisons between and within the different participant groups suggest that action effect outcome monitoring is severely undermined by orbitofrontal damage and is impacted, but not devastated in patients with LPFC lesion. These findings are discussed in relation to the performance monitoring neural network, predictive processing, the cognitive map of a state space, and action effect experimental paradigms in general.