This systematic review investigated the physiological and behavioral indicators of arousal, cognitive load, and emotional processing within the context of nonverbal behavior, aiming to inform the development of a nonverbal behavior–focused therapeutic intervention. 69 empirical studies encompassing 6,399 participants were identified through SCOPUS, Web of Science, and ProQuest for publications from 2014 to 2024. Inclusion criteria targeted healthy adults (≥18 years) and examined nine nonverbal channels: facial expressions, gestures, posture, body orientation, movement, paralanguage, proxemics, haptics, oculesics, appearance, and psychophysiology. A descriptive analysis revealed a rich spectrum of nonverbal behaviors associated with physiological arousal, cognitive load, and emotional responses across these channels. This review underscores the promise of harnessing nuanced nonverbal cues to enhance therapeutic outcomes and deepen understanding of human affective and cognitive processes.