Fear is a defensive state that promotes survival by coordinating behavioral and physiological responses to threat. Salient aversive stimuli can elicit innate defensive reactions and shape long-lasting memories of fearful events. Both rodents and primates exhibit defensive behaviors such as flight, shelter seeking, and freezing when confronted with visual threats. Extensive research in rodents over recent decades has advanced our understanding of the neural circuits of fear, but the mechanisms underlying visually guided defensive behaviors in primates remain poorly understood. Studying these processes in nonhuman primates may help develop effective treatments for disorders associated with maladaptive fear memories. Here, we evaluated the relationship between defensive behavior and hippocampal oscillations in marmosets exposed to neutral and aversive visual stimuli. We found that exposure to aversive stimuli increased fixed gaze toward the threat, reduced vigilance, restricted spatial occupancy and enhanced hippocampal gamma power. Conversely, neutral stimuli resulted in homogeneous exploratory behaviors without altering gamma activity. These results suggest that the hippocampus contributes to online threat evaluation and provide a framework for investigating how defensive behaviors guide the formation of long-lasting fear memories in primates.