The widespread adoption of mobile technologies has exacerbated their utilization in educational environments. Multitasking in the classroom is a common practice and deserves further investigation to understand its antecedents. Yet, rare studies have addressed this issue based on the theory of planned behavior framework. To this end, the current research focused on the antecedents of in-class off-task multitasking from the lens of the theory of planned behavior and its relation to perceived learning. An integrative, comprehensive model was utilized for this aim. Employing a cross-sectional survey design, the data were collected from 246 university students. The model was assessed using SmartPLS 3.2.7 in partial least square structural equation modeling (PLS-SEM). The research revealed that the theory of planned behavior was a valuable framework for understanding behavioral, normative, and control determinants of in-class off-task multitasking and its relation to perceived learning. Specifically, attitude towards multitasking, prescriptive and descriptive norms, and perceived behavioral control significantly contributed to the prediction of multitasking behavior and perceived learning. Moreover, fear of missing out, attitudes toward using digital devices during lectures, multitasking self-efficacy, and working memory capacity exhibited significant and indirect predictive effects on multitasking. While gender did not impact multitasking in the classroom, the study demonstrated a negative association between age and multitasking. The results are discussed, and implications are provided for educators to address in-class off-task multitasking behavior. The study indicated that university students must acknowledge that multitasking is unachievable without declining performance despite their belief in their ability to multitask successfully. Based on the results, we suggest that students should be informed about the limitations of human cognitive architecture. Some interventions to alter attitudes are also recommended.