Extracellular signal-regulated kinase (ERK) signal transduction is known to be associated with neurogenesis and neuronal differentiation and as such may be related to the synaptic plasticity associated with cognitive function. Although antipsychotic drug studies have suggested a potential role for the ERK cascade in schizophrenia, the mechanistic basis is unknown. The maternal immune activation (MIA) rat model is a well-known to simulate many of the clinical symptoms of schizophrenia, including cognitive deficits, but a role in this model for dynamic changes in ERK has not been established. In this study, polyinosinic:polycytidylic acid was administered to rats intravenously at a dose of 10 mg/kg on embryonic day 9.5 to produce MIA. The effect of MIA on behavior and ERK phosphorylation within the prefrontal cortex and the hippocampus of adolescent and adult offspring were explored. We also examined neurofilaments, a marker of neurogenesis, which have been reported to be modulated by ERK signaling. The results demonstrate an age- and region-specific profile of ERK expression and phosphorylation and suggest possible relationships among ERK, neurofilament expression, and cognitive performance in schizophrenia.