Introduction: Cognitive remediation is used to improve cognitive functioning in patients with schizophrenia. Most of the previous studies had incorporated a long duration of a rehabilitation program. This study aims to evaluate the effect of a short course and easy to implement computer-based cognitive remediation on the cognitive performance in patients with schizophrenia spectrum disorders using a randomized controlled trial design. Method: Sixty-two patients with schizophrenia spectrum disorders were enrolled in Roozbeh Hospital (Tehran, Iran) and were randomized to either receive a cognitive remediation program added to the standard pharmacological treatment (n=31) or the standard treatment alone (n=31). The remediation consisted of ten sessions of the cognitive training provided 2-3 times a week by applying the Cogpack software. The cognitive performance was assessed in attention, memory and executive function before and after the interventions by using the respective tests of the Cambridge Neuropsychological Test Automated Battery (CANTAB). Results: This study did not demonstrate any significant improvement in attention and executive function in the experimental vs control group. Nonetheless, we observed modest improvements in some aspects of visual memory (first trial memory score, F=9.152, P< 0.001, Cohen’s d=0.40; Mean errors to success, F= 6.991, P= 0.011, Cohen’s d=0.14; stages completed on first trial, F= 7.155, P= 0. 010, Cohen’s d=0.71; Total errors, F= 5.730, P= 0.020, Cohen’s d=0.53). Conclusion: We observed only modest improvements in the patients' cognitive functioning after a short-course of cognitive remediation. The short duration of the training and lack of a comprehensive rehabilitation plan may explain the findings.