We conducted an ERP study of derived relations within stimulus equivalence classes. After successful training of baseline relations, subjects performed a priming task and their ERP responses to the following prime-target pairs were registered: (a) stimuli related through symmetry, (b) stimuli nonrelated through symmetry, (c) stimuli related through symmetry-transivity combined (equivalence), and (d) stimuli nonrelated through equivalence. A P300-like component was observed in related targets, which was earlier for symmetry and later for symmetry-transitivity, whereas an N400-like effect was found in nonequivalent stimuli. The P300 delay after equivalent stimuli was interpreted as evidence that relational strength within equivalence classes is inversely related to the number of logical operations required to link the stimuli. The N400 effect for nonequivalent stimuli was congruent with previous literature, and suggests a potential overlap between the neural correlates of priming in language and stimulus equivalence.