The relation between the maturation of brain mechanisms responsible for the N400 elicitation in the event-related brain potential (ERP) and the development of behavioral language skills was investigated in 12-month-old infants. ERPs to words presented in a picture-word priming paradigm were analyzed according to the infants’ production and comprehension skills as rated by their parents. Infants with high early word production displayed an N400 semantic priming effect already at 12 months. Infants with low early word production did not show this effect, not even for those words that parents rated to be comprehended by their child. The results suggest that the very early functioning of the neural mechanisms underlying N400 generation is related to the infants’ state of behavioral language development. The possible functional relation of the N400 neural mechanisms and the infant’s word learning ability is discussed.