The ability to inhibit behavior is essential for achieving one's goals and being flexible in response to changing situations. Prior resting-state functional magnetic resonance imaging (RS-fMRI) studies in healthy people have shed light on key brain regions for inhibition performance (Lee & Hsieh, 2017; Tian et al., 2012). It is possible, but untested, that the association between RS-fMRI and inhibition performance seen in healthy controls extends to psychosis and helps predict the range of performance observed. Therefore, we are interested in the question of how inhibition performance is associated with spontaneous brain activity among psychosis patients and healthy people. We will also investigate how different the associations are between these two populations, and within psychosis patients. In this thesis, we expect that positive correlations exist between inhibition performance and spontaneous brain activity represented by RS-fMRI in specific brain regions of interest including default mode network and bilateral inferior frontal cortex. We also hypothesize that these correlations will be significantly weaker for some psychosis subgroups with greater inhibition response impairments. My thesis will fill in the gap in the literature and help characterize neural system alterations in psychosis, which are likely to be heterogeneous between different subgroups. An understanding of the difference in the associations may also help us better explain the decreased inhibition performance previously seen among psychosis patients (Ethridge et al., 2014). Comparison of the association between subgroups of psychosis patients may also illicit explanations for the different inhibition performances between these subgroups that have been previously identified (Clementz et al., 2016).