The effect of acute administration of ethanol extract of F. thoningii on anxiety and fear in Swiss white mice was studied. 30 adult Swiss white mice of both sexes were randomly divided in to three groups of 10 mice each. Group1 served as the control and was administered normal saline only. Group 2 (low dose group) was administered 10mg/kg ethanol extract of the F. thoningii, while group 3 (high dose group) was given 20mg/kg of the same extract. All animals were allowed food and water ad libitum. Neurobehavioral parameter was assessed using the light/dark transition box. The analysis of variance (ANOVA) was used to test for variability within and among groups. Results were expressed as Mean ±SEM (standard error of the mean) and probability level p<0.05 was accepted as significant. The result showed that the frequency of transition in the light/dark transition box was significantly increased in the test groups (p<0.05; p<0.01).Similarly, the Light Box Duration was also significantly increased (p<0.01) in the low and high dose groups respectively. However, the Dark box duration was significantly decreased (p<0.05; p<0.01) in the low and high dose groups compared to control. This index showed a decreased level of anxiety and fear in the test groups. This was followed by a corresponding trend of decreased frequency of stretch attend posture and duration of freezing in the light/dark transition box (p<0.01; p<0.001) compared to the control. Summarily, acute administration of ethanol extract of F. thonningii causes calmness and sedation in moderate and high doses. It is therefore likely that it reduces aggression. If the result from this finding is extrapolated to humans, F. thoningii could be used to reduce anxiety disorders.