Environmental factors such as pesticides are considered key determinants of brain damage and brain dysfunction. In the present work, we investigated the effect of an organophosphate pesticide, i.e., malathion, administrated peri- and postnatally on the antioxidant system as well as on acetylcholine esterase (AChE) activity in the brains of mice pups during the three postnatal weeks. Furthermore, we analyzed the behavior of the offspring just after weaning to assess the eventual effect of the pesticide on anxiety traits and social interaction. Concerning the biochemical biomarkers, the continuous treatment with malathion given either at a low dose of 5 mg/kg or at a medium one, 15 mg/kg, causes alterations in the activities of catalase, superoxide dismutase, glutathione S-transferase, and glutathione peroxidase, accompanied by high level of peroxidation of membrane lipids, indicating a disturbance in intracellular redox homeostasis with subsequent increased intracellular oxidative stress. The effect was more pronounced when the high dose was applied. This was also demonstrated for the activity of AChE, downregulated at all postnatal ages investigated (5, 15, and 21), whereas the low dose (5 mg/kg) did not alter this enzymatic activity which is in line with the absence of locomotor activity alteration as assessed by open field (OF). With regard to this last test, results obtained show also that the treated offspring mice develop an anxiogenic state as evidenced by open field as well as an impairment of social interaction. Altogether, these results provide an accurate characterization of the association between neurobehavioral outcomes and brain alterations following malathion administrated in gestational and lactational periods, even given at low dose, classified as safe, and indicate clearly that the developing brain is sensitively vulnerable to this organophosphate pesticide.