The negative effects of media multitasking have been addressed in previous studies, and the widespread adoption of online learning to control the outbreak of COVID-19 has further increased concerns about the media use, especially media multitasking, among adolescent students. However, very few studies have explored the protective factors against the potential negative effects of media multitasking. This study surveyed 465 secondary school students (246 girls; mean age = 15.03) with a paper-based questionnaire containing scales for media multitasking, mindfulness attention awareness, growth mindset, self-control and overall academic performance. The path analysis results showed that media multitasking negatively affected academic performance. Mindfulness and growth mindset influenced media multitasking not only directly but also indirectly, through self-control. Mindfulness and growth mindset also indirectly influenced academic performance through three mechanisms: the mediation of self-control, the mediation of media multitasking and the sequential mediation of self-control and media multitasking. The findings of this study support mindfulness and growth mindset as protective factors for media multitasking and its negative effects on academic performance, and they further indicate that self-control plays an important role in the influencing mechanisms. The implications of the study are also discussed.