This study investigated the differences in brain functional state between sustained attention and ignoring task conditions using the electroencephalography in association with sustained attention to response task (SART) performance. Multichannel electroencephalography data were obtained from 10 male healthy volunteers while performing the SART. Three multichannel linear descriptors, that is spatial complexity (Ω), field strength (Σ), and frequency of field changes (Φ), were applied to analyze three frequency bands (θ, α, and β) for sustained attention and ignoring task conditions. The experimental results showed that participants had a significantly lower Ω value in the θ and α band in the SART state. The Σ value was significantly higher in each frequency band of interest in almost all region of interest areas during SART performance. In addition, the Φ value was significantly lower in the θ band and significantly higher in the β band during the sustained attention condition. The results indicated that multichannel linear descriptors could show the differences in brain functions between sustained attention and ignoring task conditions, and might be used to evaluate disorders with an attentional dysfunction.