The classic account of object recognition, which proposes that object detection precedes categorization, was challenged by recent behavioral evidence. The present study investigated the temporal relation between object detection and categorization by employing ERP measures. Participants performed a dual-choice go/no-go task based on the outcomes of object detection and categorization. A no-go lateralized readiness potential, which indexed motor preparation, was obtained only when detection determined responding hand and categorization determined go/no-go, indicating that detection was completed earlier and thus activated preparation. Additionally, the N200 effect, which indicated the completion of go/no-go, was obtained 70 ms earlier when detection determined go/no-go than when categorization determined go/no-go. Our ERP results indicate that object detection is completed earlier than categorization, which supports the traditional models of object recognition.