Deficiency in cognitive control has been proposed as a core issue in addictive behavior, and recent advancements in cognitive neuroscience have suggested that frontal midline theta is a mechanism for cognitive control. This study examined frontal midline theta deficits in patients with heroin dependence during a Go/No-go task which explicitly involved cognitive control. Electroencephalography readings were collected from 15 male heroin addicts and 17 demographically matched healthy controls during an equal probability Go/No-go task. The findings revealed that heroin addicts responded significantly slower to the Go stimulus as compared to the healthy control. Heroin addicts also showed less frontal midline theta modulations between the Go and No-go conditions. These findings provided further evidence toward understanding the nature of drug addiction-related cognitive dysfunction.