Mobile health interventions are promising behaviour change tools. However, there is a concern that they may widen inequalities in health. This systematic review investigated differences in uptake of, engagement with, and effectiveness of mobile interventions for diet, physical activity, and sedentary behaviour based on a range of inequality indicators. The protocol was registered on PROSPERO (CRD42020192473). Six databases (CINAHL, EMBASE, ProQuest, PsycINFO, Pubmed, Web of Science) were searched. Publications were eligible for inclusion if they reported on an exclusively mobile intervention and examined outcomes by at least one inequality indicator. Sixteen publications reporting on 13 studies were included with most reporting on multiple behaviours and inequality indicators. Uptake was investigated in one study with no differences reported by the inequality indicators studied. Studies investigating engagement (n=7) reported differences by age (n=1), gender (n=3), ethnicity (n=2), and education (n=2), while those investigating effectiveness (n=9) reported differences by age (n=3), gender (n=5), education (n=2), occupation (n=1), and geographical location (n=1). Given the limited number of studies and their inconsistent findings, evidence of the presence of a digital divide in mobile interventions targeting weight-related behaviours is inconclusive. Therefore, we recommend that inequality indicators are specifically addressed, analysed and reported when evaluating mobile interventions.