Cognitive deficits, which are core manifestations in schizophrenia and exhibit a limited response to antipsychotic treatment, contribute to poor treatment outcomes and functional disability. Evidence on the effect of aerobic walking (AW) and exercise intensity on cognitive function in patients with schizophrenia is lacking. In total, 79 patients with schizophrenia were recruited for a 12-week randomized control trial and allocated to the treatment-as-usual (TAU, n = 38) and treatment-as-usual plus AW (TAW, n = 39) groups. The TAW participants joined a supervised 12-week AW program consisting of 30-min sessions five times per week while wearing a Fitbit Charge 2 device. Cognitive function was evaluated using the Brief Assessment of Cognition in Schizophrenia. After randomization, 67 (34 TAU and 33 TAW) participants joined the 12-week trial and were included in the intention-to-treat analysis. Multivariate general linear model repeated measures analysis revealed no significant time × group interaction effect on cognitive function changes between the TAU and TAW groups and a marginally significant group effect on verbal fluency (p = 0.09). The interaction effect of time and treatment group on verbal fluency (p = 0.05) was marginally significant between the high and low AW intensity groups, whereas a significant group effect on attention and processing speed (p = 0.04) was observed. Supervised 12-week AW of moderate intensity may have potential cognitive benefits for patients with schizophrenia.