Internet addiction disorder has reportedly become an important cause of health and social problems. The aim of this study was to investigate the effectiveness of cognitive-behavioral group therapy for internet addiction symptoms, quality of life, and mental health of students with internet addiction. This was a quasi-experimental study with pretest-posttest measures and a control group. The statistical population of the study consisted of all students at Tehran universities in the academic year of 2018-19. The target group was selected through an internet addiction test and a clinical interview using a targeted sampling method and was divided into experimental and control groups by randomization. The experimental group participated in fifteen 90-minute cognitive-behavioral group therapy sessions. Before, immediately after, and 3 months after the treatment, the internet addiction symptoms of both groups were evaluated to assess mental health with the IAT, quality of life (QOL), and SCL-90-R questionnaires. Data were analyzed with ANCOVA analysis using SPSS Statistics 20 software. After treatment, cognitive-behavioral therapy groups showed reductions in internet addiction scores (p < 0.05). Results showed that the cognitive-behavioral group therapy was effective for improving quality of life (p < 0.05) and mental illnesses (p < 0.05) in students with internet addiction. Cognitive-behavioral group therapy can enhance awareness and mental health of students with internet addiction. Therefore, this intervention can be used as a beneficial treatment to reduce internet addiction symptoms and improve the condition of people with behavioral addictions such as internet dependency.