Among the three learning domains, i.e., cognitive, affective, and psychomotor, the cognitive learning domain has been received most educators' work, leaving ample of research gaps for the affective and psychomotor domain. This paper reviews the affective learning domain and methods for measuring affective learning objectives, particularly in online courses where issues related to evaluating affective performance could become even more challenging. The paper first starts with a discussion of the affective learning domain in education. Then it analyzes the challenges in and methods for measuring affective learning objectives with a focus on online environment. The paper concludes with suggestions and recommendations on the kinds of methods to measure affective learning outcomes in online settings.