<p>Cognitive workload refers to the mental effort required to perform a task and plays a vital role in cognitive functioning and daily decision-making. The precise estimation of cognitive workload can increase efficiency and decrease mental errors. EEG signals are non-invasive and trustworthy, containing useful information about mental and cognitive tasks, and are very effective in measuring cognitive workload. This study aims to classify various cognitive workload levels using EEG signals, primarily by channel selection based on the Pearson Correlation Coefficient, to reduce computational complexity and facilitate real-time applications. As time–frequency decomposition techniques can provide simultaneous time and frequency information for more accurate analysis, three techniques were adopted: Maximal Overlap Discrete Wavelet Transform (MODWT), Empirical Mode Decomposition (EMD), and a hybrid approach combining both. After decomposition, ten statistical features were extracted, and the Improved Distance Evaluation technique was employed to select the most critical features. Classification was performed on these features using three classifiers: Support Vector Machine (SVM), K-Nearest Neighbors, and Decision Tree. The findings revealed the important role of frontal EEG channels in assessing cognitive workload. Additionally, the combined use of MODWT and EMD with the SVM classifier yielded the best classification accuracy for both binary and three-class classification scenarios. The results indicate that the optimal choice of channels, combined with time–frequency decomposition methods, can significantly enhance classification accuracy while reducing system complexity in estimating cognitive workload.</p>