Background: Many instructors transitioned their courses from face-to-face environments to computer-mediated learning environments (CMLEs) following the onset of the coronavirus disease 2019 (COVID-19) pandemic. However, little was known about how teleconferencing platforms and their corresponding functions affect student learning when the COVID-19 pandemic began. Objectives: The aim of this study was to provide more clarity on the conditions through which online teleconferencing platforms influence student achievement. More specifically, this study investigated how displaying lecture-relevant and lecture-irrelevant messages in a chat box during a video lecture delivered via the Zoom teleconferencing platform affected student learning and note taking. Methods: Participants viewed the video lecture either with (relevant or irrelevant) or without messages appearing in the chat box of the Zoom window. Participants completed a learning test immediately following the lecture. Results and Conclusions: No difference regarding student achievement was observed between the three groups. However, results revealed that students in the relevant-lecture messages group reported a higher extraneous cognitive load than the other groups even if they reported positive attitudes about the messages appearing on the chat box. Students in the lecture-relevant group also recorded more notes during the lecture compared to the two other groups, but this result did not reach significance. This study extends previous research that investigated how messaging influences learning in classroom settings. Findings suggest that allowing relevant discussions is not the best strategy to promote learning in CMLEs as this information seems to compete with the other relevant information being presented during the ongoing lecture.