Background: Although negative beliefs have been found to be associated with worry symptoms and depressive rumination, negative beliefs have yet to be examined in relation to post-event processing and social anxiety symptoms. Aims: The purpose of the current study was to examine the psychometric properties of the Negative Beliefs about Post-Event Processing Questionnaire (NB-PEPQ). Method: A large, non-referred undergraduate sample completed the NB-PEPQ along with validation measures, including a measure of post-event processing and social anxiety symptoms. Results: Based on factor analysis, a single-factor model was obtained, and the NB-PEPQ was found to exhibit good validity, including positive associations with measures of post-event processing and social anxiety symptoms. Conclusions: These findings add to the literature on the metacognitive variables that may lead to the development and maintenance of post-event processing and social anxiety symptoms, and have relevant clinical applications.