Many studies suggest a protective role of phenolic compounds in mood disorders. We aimed to assess the effect of Euterpe oleracea (açaí) seed extract (ASE) on anxiety induced by periodic maternal separation (PMS) in adult male rats. Animals were divided into 6 groups: control, ASE, fluoxetine (FLU), PMS, PMS+ASE, and PMS+FLU. For PMS, pups were separated daily from the dam for 3 h between postnatal day (PN) 2 and PN21. ASE (200 mg·kg⁻¹·day⁻¹) and FLU (10 mg·kg⁻¹·day⁻¹) were administered by gavage for 34 days after stress induction, starting at PN76. At PN106 and PN108, the rats were submitted to open field (OF) and forced swim tests, respectively. At PN110, the rats were sacrificed by decapitation. ASE increased time spent in the center area in the OF test, glucocorticoid receptors in the hypothalamus, tropomyosin receptor kinase B (TRKB) levels in the hippocampus, and nitrite levels and antioxidant activity in the brain stem (PMS+ASE group compared with PMS group). ASE also reduced plasma corticotropin-releasing hormone levels, adrenal norepinephrine levels, and oxidative damage in the brain stem in adult male offspring submitted to PMS. In conclusion, ASE treatment has an anti-anxiety effect in rats submitted to PMS by reducing hypothalamic–pituitary–adrenal axis reactivity and increasing the nitric oxide (NO)–brain-derived neurotrophic factor (BDNF)–TRKB pathway and antioxidant defense in the central nervous system.Novelty ASE has anti-anxiety and antioxidant effects in early-life stress. ASE reduces hypothalamic–pituitary–adrenal axis reactivity. The anxiolytic effect of ASE may involve activation of the NO–BDNF–TRKB pathway in the central nervous system.