Introduction. Nigella sativa is a commonly used traditional medicine which has been shown to have antioxidant properties. However, its supplementation in patients of clinical trials showed conflicting results. Materials and Method. Relevant articles were searched through PubMed/Medline, SCOPUS, and Google Scholar databases using "Nigella sativa" or "black seed" or "black caraway" or "thymoquinone" and "oxidative stress" or "antioxidant" and "clinical trial" keywords. Randomized, placebo-controlled human interventions using Nigella sativa were included in this study. The methodological quality of studies was assessed using Jadad's quality scales. Results. Five studies using 293 subjects met the inclusion criteria. The overall quality of all included trials was determined based on the low risk of bias and the high quality of reported information (Jadad score ≥ 3). Meta-analysis of 293 eligible subjects showed that treatment with Nigella sativa improved the superoxide dismutase (SOD) level (48.18; 95% CI 30.29 to 66.08; p<0.01), but there was no significant effect on the malondialdehyde (MDA) level (-5.32; 95% CI -1.19 to 0.128; p=0.114) and total antioxidant capacity (TAC) level (0.219; 95% CI -0.136 to 0.573; p = 0.227). Conclusion. This meta-analysis suggests that Nigella sativa supplementation in humans may benefit as an antioxidant by increasing SOD levels but has no significant effect on the MDA level and TAC level.