In this study, it was aimed to investigate the primary mathematics teacher candidates' perceptions about the equal sign within the scope of neuroscience studies. To reveal their perceptions about the equal sign, three types of addition operations were asked to the participants: a+b=[], []=a+b, a+b=[]+c. Their brain waves were recorded by EEG device named as Neuron-Spectrum 4. Moreover, their ideas about the types of the questions were asked to support EEG data. As a result, it was found that the teacher candidates had more cognitive activity in parietal lobe while solving the questions of type two and three. In addition to this, they also showed more cognitive activity in frontal lobe for the type three questions. EEG results reveal that they had difficulty to answer these questions than the questions of type one as they also wrote on the interview form.