Ongoing low-frequency EEG activity has long been associated with ERP components and their cognitive processing interpretations, yet few studies have directly investigated the prestimulus low-frequency EEG–ERP relationships, particularly within the auditory domain. The present study assessed the delta (1–3 Hz) and theta (4–7 Hz) bands individually, and their prestimulus influence on five subsequent components (P1, N1, P2, N2, and P3) within an equiprobable auditory Go/NoGo paradigm. At the nine central sites, accepted trials were sorted according to their ascending vertex prestimulus spectral band amplitude, and ERPs were derived from the upper and lower sorted thirds. The within-subjects analyses included amplitudes and latencies for both Go and NoGo responses, and Go response speed. Only component amplitudes showed effects of high/low prestimulus EEG level. Delta globally modulated the five components — all amplitudes were more positive with high prestimulus delta, regardless of stimulus condition. Theta did not influence P1, but inversely modulated P2 and P3 regionally, and produced stimulus-specific effects in N1, N2, and P3. Low prestimulus theta produced greater NoGo N2 and Go P3, and reduced NoGo P3 responses, each of these suggesting appropriately enhanced cognitive processing. Taken together, these effect patterns differentially implicate prestimulus delta and theta band activity in the determination of ERP component amplitudes and the cognitive processing associated with them.