Purpose: Political tension, as expressed by mass movements such as the Occupy Central movement (2014) in Hong Kong, is a potential but understudied structural factor of population mental health. Methods: A random population-based telephone survey anonymously interviewed 344 Hong Kong Chinese adults aged 18–65 years during the 2 weeks since the termination date of the 2-month-long Occupy Central movement (15/12/2014). Linear regression models were fit using mental distress (depression, anxiety and negative mood) and self-perceived changes in mood/sleeping quality as dependent variables. Results: Prevalence of participation in the movement was 10.5% (self), 17.7% (family members/relatives), and 34.0% (peers); 8.5% had participated for ≥2 days. Young age, but not participation, was associated with mental distress. In adjusted analysis, three types of responses to the movement (worry about safety, negative emotional responses to media reports, and conflicts with peers about the movement) and emotional responses to local political situations were significantly associated with all/some of the dependent variables related to mental distress. The variable on emotions toward local political situations was correlated with the three responses to the movement; it fully mediated the associations between such responses and mental distress. Conclusion: Many citizens participated in the movement, which was led by youths and might have increased the general public’s mental distress. Negative personal responses to the movement and emotions toward political situations were potential risk factors. As the political tension would last and political pessimism is globally found, politics may have become a regular and persistent structural risk factor negatively affecting population mental health.