Objectives <p>Tinnitus affects millions worldwide. Its neural mechanisms remain unclear. This study aimed to explore the causal relationships between brain functional networks and tinnitus risk using Mendelian randomization (MR) analyses.</p> Methods <p>We performed MR analyses using brain activity data from resting-state functional magnetic resonance imaging (rs-fMRI) and genetic data from genome-wide association studies (GWAS). A total of 191 brain features, including amplitude traits and functional connectivity measures, were selected based on their genetic associations.</p> Results <p>Forward MR analyses showed that increased activity in the parietal and inferior frontal regions was associated with a 41% reduction in tinnitus risk (OR = 0.59, <i>p</i> = 1.8 × 10^–4). In contrast, increased activity in the precuneus, angular gyrus, and frontal areas was linked to a 49% increase in tinnitus risk (OR = 1.49, <i>p</i> = 8.9 × 10^–4). Activities in the parietal and inferior frontal regions were negatively correlated with tinnitus risk (OR = 0.72, <i>p</i> = 0.0037). Additionally, higher activity in the parietal, frontal, and temporal regions doubled the risk (OR = 2.02, <i>p</i> = 0.015). Reverse MR showed that stronger connectivity between frontal and temporal regions was inversely related to tinnitus risk (beta = − 0.056, <i>p</i> = 0.049).</p> Conclusions <p>Specific brain activity and connectivity patterns are causally linked to tinnitus.</p>