Health behavior theories have proven effective in understanding individuals' COVID-19-related protective behaviors. This study aimed to identify predictors of mask-wearing behavior during the COVID-19 pandemic in Armenia using the constructs of the Health Belief Model (HBM) and the Theory of Planned Behavior (TPB). We conducted a telephone survey in 2021 in a nationwide sample of adult Armenian population selected via stratified two stage random sampling. The survey questionnaire included questions on socio-demographic characteristics, COVID-19 protective behaviors, knowledge, vaccination status, and constructs from the HBM and TPB. Mask-wearing in public places in the past 14 days was analyzed using multivariable logistic regression with variable entry in blocks. The majority of 3,439 respondents were females (71.2%). The mean age was 49.44 years. Approximately 52% always/usually wore masks. The final logistic regression model, incorporating socio-demographic characteristics, COVID-19 knowledge, vaccination status, HBM constructs, and perceived social norm, explained 23% of the variance in mask-wearing behavior. Age, perceived threat, benefits, barriers, cues to action, and social norm were significantly and independently associated with mask-wearing. While several socio-demographic factors and theory-based constructs emerged as significant predictors, their limited explanatory power highlights the importance of exploring additional factors influencing mask-wearing behavior. The study stresses the role of social norms in shaping COVID-19 preventive behaviors and provides important evidence for public health interventions globally in Armenia, and other post-Soviet countries, where theory-based approaches to health behavior change are scarce.