Emotion regulation emerges early in development and unfolds primarily within caregiver–infant interactions that support infants’ ability to manage stress and return to physiological balance. Neurophysiological measures may provide insight into the mechanisms underlying these early regulatory processes. One candidate index is delta–beta EEG coupling (DBC), which has been proposed to reflect coordination between slower oscillatory activity associated with subcortical affective processes and faster oscillations linked to cortical regulatory control. However, most studies in infancy have examined DBC at rest or in non-relational contexts. The present study investigated DBC during the Still-Face paradigm, which elicits socio-emotional stress through a temporary disruption of caregiver responsiveness. Forty-nine infants aged 6–12 months participated in a laboratory assessment during which EEG activity was recorded continuously across the Play, Still-Face, and Reunion episodes. Infants’ negative emotionality was coded second-by-second using the ICEP system. DBC showed site-specific modulation, reflected in a significant Episode × Site interaction (F = 6.08, p = .003), with higher frontal than central coupling during the Still-Face episode (p = .003) and an increase in central DBC from Still-Face to Reunion (p = .042). Linear mixed-effects models further indicated that central DBC was differentially associated with infants’ negative emotionality across episodes (F = 3.28, p = .042): higher negative emotionality associated with lower central DBC during Still-Face (p = .015) and higher central DBC during Reunion (p = .005). Overall, these findings suggest that DBC may index context-dependent neural coordination during early socio-emotional stress and recovery in infancy.