Tracking and updating emotional information in daily language use is essential for successful comprehension and communication. Using an event-related potential technique, we investigated how the updating of emotional information was influenced by changes in topic with two-pair conversational discourses. The first pair established a topic and a kind of emotional information. The second pair either maintained or changed the topic of the first pair. The description of the topic within the second pair contained a critical word that either maintained or shifted the emotional valence of the first pair. Event-related potentials (ERPs) were recorded for both the topic words and the emotion words. We found that the topic-shifted words elicited a larger P2, a larger N400, and a larger late positive component (LPC) than the topic-maintained words. More importantly, we found that emotion updating elicited an enhanced sustained N400 in the topic-maintained discourses. On the other hand, emotion updating induced a pronounced LPC in the topic-shifted discourses. These results suggest that topic shift captures more cognitive resources for its own processing and new substructure building, which further affects the processing of emotion updating. Our findings demonstrated an active use of topic information in guiding emotion updating during natural language comprehension.