There has been a growing burden of anxiety among Nepalese adolescents. Social anxiety in particular is one of the commonly reported symptoms indicating mental health problem among adolescents. The purpose of this study was to assess social anxiety, and identify how social support, emotion regulation and mindfulness uniquely contribute to social anxiety among adolescents in Birgunj, Nepal. The study was conducted by using a self-administered questionnaire among 384 adolescents (65.4% boys; M = 16.05 years, SD = 1.39) studying at secondary schools of Birgunj. Results show that there was a positive correlation between social anxiety symptoms and age, and girls reported more symptoms. Traits such as non-acceptance of emotions, lack of clarity and lack of awareness of emotions were related to increased social anxiety; while acting with awareness, non-reactivity, and better ability to describe emotions was related to decreased social anxiety. Finally, more social support from close friends was related to lower social anxiety. These results suggest that improving emotion regulation, dispositional mindfulness, and social support may be helpful for adolescents who are at risk of, or are suffering from, social anxiety.