Background: Since COVID-19 is a new disease with devastating effects worldwide, its emergence and spread aroused confusion, anxiety, and fear among the public. Objectives: The present study aimed to evaluate the effectiveness of paradox therapy on the COVID-19 anxiety in adult population in Jahrom, Iran. Methods: This research was a quasi-experimental study with a pretest-posttest design and a two-month follow-up. The research population encompassed all individuals willing to participate in the present study who were residing in Jahrom during 2020-2021. According to the COVID-19 Anxiety Scale, 30 participants with high levels of COVID-19 anxiety were selected using the convenience sampling method and were randomly assigned to experimental (n = 15) and control (n = 15) groups. The experimental group received eight sessions of paradox therapy; however, the control group remained on the waiting list. The research tools included structured clinical interviews and the COVID-19 Anxiety Scale. Finally, the collected data were analyzed using Friedman’s statistical method. Results: The results showed that paradox therapy was effective in decreasing COVID-19 anxiety (P = 0.001) and its psychological (P = 0.001) and physical (P = 0.002) symptoms, and the scores of the COVID-19-induced psychological and physical symptoms in the posttest phase were significantly lower in the intervention group than the control group (P < 0.001). The decrease was noticed in the follow-up phase as well. Conclusions: According to the results, paradox therapy can effectively reduce anxiety and its psychological and physical symptoms due to COVID-19.