Objectives: This 2-month cohort study aimed to investigate the changing prevalence and factors associated with COVID-19-related workplace bullying among the general workers in Japan. Methods: A baseline survey was conducted of 4,120 full-time workers at Time 1 (March 2020) and they were invited to a follow-up survey at Time 2 (May 2020) after the outbreak of COVID-19 in Japan. The prevalence of COVID-19-related workplace bullying was compared between Time 1 and Time 2 by using McNemar's test. Multiple logistic regression analysis was conducted to investigate the associations between occupation (health care and non-health care workers), socioeconomic status, living in areas under the national emergency announcement, workplace measures against COVID-19, occupational class, chronic physical comorbidities, chronic mental comorbidities, and COVID-19-related workplace bullying at Time 2, adjusting for that at Time 1. Results: A total of 1,421 responded to the survey at Time 2. Data from 996 respondents after excluding 36 who retired during the follow-up were analyzed. The prevalence of COVID-19-related workplace bullying increased more than double from Time 1 (2.8%) to Time 2 (6.5%). Being a manual worker (OR=3.80), having higher education (OR=2.37), and having chronic physical comorbidity (OR=2.11) was significantly associated with the COVID-19-related workplace bullying at Time 2. Conclusions: COVID-19-related workplace bullying increased during the outbreak of COVID-19 in Japan. A lower-class occupation (manual workers) and having chronic physical comorbidity may be associated with greater victimization of COVID-19-related workplace bullying, while those with high educational attainment may be more sensitive to it.