Attachment security describes a sense of safety and security felt by individuals and promotes mental health. The mechanism by which attachment security buffers against psychological threat remains unclear, however. Here, we explored how attachment security attenuates the response to threatening information using a signal detection theory (SDT) and event-related potentials (ERPs) approach. Participants were assigned to an attachment security priming condition or a control condition. After a priming procedure, behavioral data and electroencephalography (EEG) signals were recorded while participants categorized threatening and neutral pictures. Our behavioral results revealed that attachment security biased participant responses to categorizing the two types of pictures; participants in the control condition exhibited a tendency to categorize stimuli as threatening, whereas those in the attachment security condition tended to categorize stimuli as neutral. Meanwhile, attachment security priming modulated early attention processes, reflected by an increased P200. The findings reported here suggest that attachment security buffers against external threats by modulating individual response preferences, the effects of which manifest in the early stages of attentional processing.