When speakers name a picture (e.g., “duck”), a distractor word phonologically related to an alternative name (e.g., “birch” related to “bird”) slows down naming responses compared with an unrelated distractor word. This interference effect obtained with the picture–word interference task is assumed to reflect the phonological coactivation of close semantic competitors and is critical for evaluating contemporary models of word production. In this study, we determined the ERP signature of this effect in immediate and delayed versions of the picture–word interference task. ERPs revealed a differential processing of related and unrelated distractors: an early (305–436 msec) and a late (537–713 msec) negativity for related as compared with unrelated distractors. In the behavioral data, the interference effect was only found in immediate naming, whereas its ERP signature was also present in delayed naming. The time window of the earlier ERP effect suggests that the behavioral interference effect indeed emerges at a phonological processing level, whereas the functional significance of the later ERP effect is as yet not clear. The finding of a robust ERP correlate of phonological coactivation might facilitate future research on lexical processing in word production.