Background: The COVID-19 pandemic has aroused fear and anxiety in many people worldwide. Objectives: The study was conducted to measure the efficacy of internet-based cognitive-behavioral therapy (ICBT) for mental health, post-traumatic stress disorder (PTSD), and obsessive-compulsive disorder (OCD) in students with COVID-19 anxiety. Methods: This semi-experimental study was conducted as a pre-post-test with a control group. The statistical population of the research included the students of the Tarbiat Modares University in the academic year 2021. To collect the required data, 30 students with COVID-19 anxiety were randomly allocated to control (n = 30) and experimental (n = 30) groups. The data collection tools included a questionnaire on COVID-19 anxiety, mental health, PTSD, and OCD. Following the pre-test, ICBT was implemented in eight 90-minute sessions for the experimental group. To analyze the data, SPSS software version 24 and the multivariate covariance analysis were used. Results: It was revealed that ICBT could significantly increase mental health (M = 54.26, F = 33.38) and reduce PTSD (M = 67.20, F = 30.43) and OCD (M = 116.13, F = 19.11) in students with COVID-19 anxiety (P < 0.01). Conclusions: In general, it can be acknowledged that ICBT has promoted mental health and reduced PTSD and OCD. Accordingly, it is suggested to hold workshops and virtual programs by psychologists for students with COVID-19 anxiety.