Given the increasing popularity of online learning, the study of the user experience in online courses is relevant for the design of meaningful online learning. While there exist many checklists for online course evaluation, they focus on different items and lack consensus of common usability factors. Traditional usability studies focus on technology issues; however, as literature shows, they neglect pedagogical and social usability. In addition, online courses have been studied with undergraduate or graduate students neglecting the population of older adults (55+ years old). In this study, we explored usability factors regarding social, technical, and pedagogical items with a focus on older adult learners. We applied the mental model approach to understand the adult learner experience by collecting qualitative data. The results present the following key factors: (a) usability related to social presence, instructor, and adult learner interaction; (b) usability related to technology, including access to the course and course navigation; and (c) usability related to pedagogy including learning objectives, content organization, instructional activities, and assessment. These findings have implications for instructors who are involved in teaching online courses for older adult learners.