To assess prefrontal brain network abnormality in adults with obstructive sleep apnea (OSA), resting‐state functional near infrared spectroscopy (rs‐fNIRS) was used to evaluate 52 subjects, including 27 with OSA and 25 healthy controls (HC). The study found that patients with OSA had a decreased connection edge number, particularly in the connection between the right medial frontal cortex (MFG‐R) and other right‐hemisphere regions. Graph‐based analysis also revealed that patients with OSA had a lower global efficiency, local efficiency, and clustering coefficient than the HC group. Additionally, the study found a significant positive correlation between the Montreal Cognitive Assessment (MoCA) score and both the connection edge number and the graph‐based indicators in patients with OSA. These preliminary results suggest that prefrontal rs‐fNIRS could be a useful tool for objectively and quantitatively assessing cognitive function impairment in patients with OSA.