Paranoia is common and distressing in the general population and can impact on health, emotional well-being and social functioning, such that effective interventions are needed. Brief online mindfulness-based interventions (MBIs) have been shown to reduce symptoms of anxiety and depression in non-clinical samples; however, at present, there is no research investigating whether they can reduce paranoia. The current study explored whether a brief online MBI increased levels of mindfulness and reduced levels of paranoia in a non-clinical population. The mediating effect of mindfulness on any changes in paranoia was also investigated. One hundred and ten participants were randomly allocated to either a 2-week online MBI including 10 min of daily guided mindfulness practice or to a waitlist control condition. Measures of mindfulness and paranoia were administered at baseline, post-intervention and 1-week follow-up. Participants in the MBI group displayed significantly greater reductions in paranoia compared to the waitlist control group. Mediation analysis demonstrated that change in mindfulness skills (specifically the observe, describe and non-react facets of the FFMQ) mediated the relationship between intervention type and change in levels of paranoia. This study provides evidence that a brief online MBI can significantly reduce levels of paranoia in a non-clinical population. Furthermore, increases in mindfulness skills from this brief online MBI can mediate reductions in non-clinical paranoia. The limitations of the study are discussed.