Introduction: Low back pain (LBP) is a common musculoskeletal disorder (MSD) that leads to a variety of negative consequences. The prevalence of LBP was found to be high worldwide. Individuals have been forced to remote studying or working conditions during the coronavirus disease 2019 (COVID-19) pandemic, exposing them to the risk factors of LBP to a greater extent. This is a cross-sectional study conducted among 623 adults and aimed to assess LBP intensity and prevalence among adults in Malaysia before and during the COVID-19 lockdown and to identify the association between demographic, physical and psychological factors with LBP. Methods: A self-administered questionnaire composed of 36 questions regarding demographic characteristics, physical activities and psychological aspects was distributed to the public. Pearson’s Chi-square and Fisher Exact tests were performed using collected data to assess the association between LBP intensity and various risk factors. Results: The prevalence of LBP increased from 64.4% before the lockdown to 83.5% during the lockdown. LBP intensity significantly increased during the lockdown. Before lockdown, factors associated with LBP intensity included gender and stress level. While during the lockdown, age, gender, occupation, time spent on computer use, ergonomics as well as stress level affected the intensity of LBP. Conclusion: The present study showed that the COVID-19 lockdown has contributed to the increase in both the prevalence and intensity of LBP among Malaysians. The identified risk factors include age, gender, occupation, duration of sitting and computer use, adherence to ergonomic recommendations, and stress level.