This paper presents a back-propagation neural network for detecting a quadratic trend involved in a time series of random signals. Synthetic data and real pressure data with a trend are used to elucidate the detection ability of wavelet-based method, regression analysis and the proposed model. Both the proposed model and the regression analysis have a comparably high accuracy to remove the quadratic trend from all sets of synthetic signals than the wavelet-based model. The present approach can be applicable for identifying a higher-order polynomial trend from a time series of real or synthetic data.