Electrophysiological correlates of human reliability in visual response tasks were investigated in 16 healthy subjects using electroencephalographic (EEG) spectral power and event-related potentials (ERP). Human reliability was first determined by calculating individual reaction accuracy in order to split the entire group into high reliability (HR) and low reliability (LR) subgroups, each with eight subjects. The EEG activities of testing subjects were measured at rest condition for 5 min, and during a modified Eriksen flanker task. Artifact-free EEG segments were used to compute the distribution of EEG at varied frequency bands as well as to detect peak and latency of ERPs of the flanker task. Our results showed that subjects with LR exhibited higher alpha band EEG power at the frontal recording site. Additionally, LR group revealed lower P300 amplitude and predominantly longer P300 latency at centro-parietal recording site than those of the HR group. These findings implied that higher alpha band EEG power at frontal and smaller amplitude, longer latency P300 component of ERP measures at centro-parietal might reveal the trait of lower reliability in healthy controls during visual tasks.