The Bivalent Evaluation Fear Hypothesis posits that fear of positive evaluation (FPE) and fear of negative evaluation (FNE) are two independent core characteristics of social anxiety. However, whether they rely on dissociable and/or shared neural mechanisms in the processing of social motivation remains unclear. By employing the Social Incentive Delay Task combined with EEG, we found that during the anticipation phase, individuals with high FPE exhibited ”generalized over-engagement toward evaluative situations”—enhanced conflict monitoring (N2) and motivational preparation (CNV) in response to both reward and punishment cues. In contrast, individuals with high FNE displayed ”specific threat vigilance with generalized motivational withdrawal”—demonstrating enhanced N2 specifically to punishment cues, along with reduced CNV to both reward and punishment cues, consistent with a profile of defensive motivational inhibition. During the feedback phase, both groups displayed a common deficit: reduced delta and theta oscillations in response to socially accepting feedback, indicating a shared impairment in deep reward integration. These findings demonstrate that FPE and FNE are associated with fundamentally distinct neuro-affective preparatory patterns during anticipation: one characterized by a generalized, vigilant over-mobilization, and the other by specific threat vigilance coupled with generalized reduction in motivational engagement. At the same time, the shared delta and theta deficits during the feedback phase constitute a core neural marker, which may underlie the common difficulty of both groups in translating positive social outcomes into adaptive motivational behaviors. This study deepens our understanding of evaluation fears and provides critical neural evidence in support of the Bivalent Evaluation Fear Hypothesis.