Many adolescents worldwide suffer from stress or unhealthy emotional states such as depression. There is a trend toward limited physical contact via social distancing practices that developed during the coronavirus disease 2019 (COVID-19) pandemic. An experimental study aimed at investigating the effects of a mindfulness program on stress, concentration, self-esteem, and self-control in high school students. A 10-week mindfulness intervention was provided to the experimental group (n = 89) from September-November 2020, while the control group (n = 89) received general health education. Four weeks after the program, the experimental group showed reduced stress and improved concentration, self-esteem, and self-control compared to baseline.