Social campaigns are persuasive messages that attempt to communicate positive ideas and practices. One of the main challenges in designing effective social campaigns is the need to compete with other advertisements for viewers' attention. One of the most widely used methods of drawing attention to social advertising is the use of negative emotions. However, the effectiveness of negative emotional appeals in social campaigns is still a topic of debates. The aim of the study was to use both declarative and neural (EEG) measures to examine whether increasing the intensity of negative emotions in a social campaign enhances its effectiveness linearly or only to a certain level (curvilinear relation). The experimental study was conducted (N = 62) with road safety campaign, using three different levels of negative emotional intensity. The results showed that even though advertising with the strongest negative stimuli evoked the strongest negative emotions, it had no significantly stronger influence on behavioral intention (driving less risky) than moderately negative stimuli. Moreover, neural reaction to the negative stimuli in advertising depended on driving style-people with risky driving style payed less attention to more threatening message (higher beta oscillations).