Barriers to accessing offline healthcare may discourage patients from undergoing mammography screening. Online patient–provider communication (OPPC) offers a supplementary health resource that can complement traditional medical encounters and facilitate mammography screening. This study examines how offline healthcare barriers influence mammography screening, taking into account OPPC as an independent variable and cancer fatalism and patient activation as two mediators. Data from the 2017, 2018, and 2020 iterations of the Health Information National Trends Survey were used for this study. Results showed that OPPC was positively linked to mammography screening. Offline healthcare barriers had a negative association with patient activation and subsequent mammography behaviors. Moreover, offline healthcare barriers and OPPC were associated with mammography screening through serial mediation of cancer fatalism and patient activation. This study has important implications for encouraging mammography screening.