Eclipta alba (Linn) (EA) has been found useful ethnomedicinally in the treatment of many medical conditions especially mental disorders. Aims of the Study: This study aimed to evaluate the acute toxicity profile, behavioural activity, antipsychotic and mechanism of action of the Aqueous extract of Eclipta alba (AEA). Methodology: Using Lorke’s method the LD50 of AEA was 1,264 mg/kg (i.p) and 3,807 mg/kg (oral) respectively was obtained, which shows that AEA was moderately toxic. The AEA was analysed using standard procedure: novelty-induced behaviour (NIB), through intraperitoneal route shows that AEA (p < 0.0001) exhibits depressant effects on the central nervous system (CNS), while the antipsychotic models (catalepsy, amphetamine-induced hyperlocomotion, swimming-induced grooming and apomorphine-induced climbing tests), (p < 0.0001) reveals that it possesses antipsychotic properties. Conclusion: This study shows that the mechanism of action of AEA (antagonist model: haloperidol, atropine and cyproheptadine) (p < 0.0001) probably mediated via histaminergic, serotonergic and dopamine pathways, which provides scientific support for the ethno-medicinal use of the plant in the treatment of mental illness.