This work presents Online dictionary learning (DL) methods for landmine classification using Ground penetrating radar (GPR) data. A novel Drop-Off MINi-batch Online Dictionary Learning (DOMINODL) is also developed. Experiments with real L-band GPR data show that the proposed method reduces learning time by 36-93%, increases accuracy by 4-28% over state-of-the-art DL approaches and outperforms a Convolutional Neural Network (CNN) classifier.