We aimed to investigate attentional resources distribution in traumatic brain injury (TBI) patients. Auditory event-related potentials (ERPs) were recorded from 35 severe TBI patients in post-acute care, and 35 age- and gender-matched controls using an auditory oddball paradigm under passive (ignore stimuli) and active (count deviants) conditions. Six components (P1, N1, P2, N2, P3, N3) in four waveforms were studied, i.e., the waveforms elicited by standard and by deviant tones in the passive and active task, respectively. In addition to alterations of latency and/or amplitude of single components, particularly of the late components N2 and P3, we observed in patients a different response pattern to task condition. We found evidence of deficits in the early stages of information processing and allocation of attentional resources. The analysis of the response to standards was crucial for detecting new aspects of attentional impairments.