Electronic health (eHealth) and mobile health (mHealth) could stimulate physical activity (PA) in a time‐efficient and cost‐effective way. This randomized controlled trial aims to investigate effects on moderate‐to‐vigorous PA (MVPA) of different combined computer‐ and mobile‐based PA interventions targeted at adults aged 50 years and over. Participants (N = 954) were randomly allocated to a basic existing computer‐based intervention (Active Plus [AP] or I Move [IM]) supplemented with one of three mobile elements being (1) activity tracker (AT), (2) ecological momentary intervention (EMI), or (3) chatbot (CB) or a control group (CG). MVPA was assessed via the SQUASH at baseline (T0), 3 months (T1), and 6 months (T2) and via accelerometers at T0 and T2. No intervention effects were found on objective (p = .502) and subjective (p = .368) MVPA for main research groups (AP/IM + AT, AP/IM + EMI, AP/IM + CB). Preliminary MVPA findings for subgroups (AP + AT, AP + EMI, AP + CB, IM + AT, IM + EMI, IM + CB) combined with drop‐out data showed potential for the computer‐based intervention AP with an integrated AT. Based on these preliminary findings, eHealth developers can be recommended to integrate ATs with existing computer‐based PA interventions. However, further research is recommended to confirm the findings as a result of the exploratory nature of the subgroup analyses.