The electroencephalogram (EEG), the brain activity of neurons in the brain, is used to record brain activity for many puiposes. It also changes depends on mental conditions because mental conditions are generated in the brain. In this study, we try to estimate the mental conditions by observing the EEG patterns. The EEG data caused by mental changes is obtained as giving the subjects animal assisted therapy. The method for estimation is AdaBoosting as the neural network. We set the input vector as EEG changes and output vector is set as mental changes. Subjects are 25 people: 19 males and 6 females (age: 21-24 years old). Previous study reveals the correlation between the EEG and the activeness, and between the EEG and the tiredness. Therefore, in this paper, we try to estimate these mental parameters by the EEG at the first step.