Background: The overuse and abuse of the Internet incur the risk of Internet addiction. Besides, as adolescents spend many hours on the Internet, their general health is at stake. Methods: The present study was a descriptive cross-sectional study. The study sample included 1000 female and male high school students in Bushehr City in 2018. The students took part in this study by completing Kimberly Young's Internet Addiction Test (IAT) and Goldenberg's Mental Health Questionnaire. The frequency, mean, and standard deviation measures were also used to explain the results, and data analysis was performed using the Chi-squared tests technique, which was also used to analyze the data and to examine the relationship among mental health and Internet addiction and logistical regression. Results: According to the results of the prevalence of Internet addiction it was found that 1.1% (10 individuals) were Internet-addicted and 33.1% (299 individuals) were at the risk of Internet addiction. The findings of this study indicated that four different areas of mental health including physical condition, anxiety, depression, and social functioning have a direct relationship with Internet addiction (P < 0.05). Conclusions: In the present study, a large percentage of the students were prone to Internet addiction. Hence, it is necessary to plan and perform preventive, controlling, and interventional measures for high school students.