Carbon nanotube electrodes were prepared by pressing a mixture of carbon nanotubes and polytetrafluoroethylene (which acted as a binder) on a stainless steel net collector, and the electrodes were subsequently activated in our self-designed plasma apparatus, using air plasma. The morphology and surface functional groups of the electrodes were characterized using scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. The results showed that the electrodes activated by air plasma possessed a rougher surface and more oxygen-containing groups than the raw electrodes, properties that were beneficial for their electrosorption performance. After 5 min of air plasma activation, the lead ion electrosorption capacity of the activated electrodes (measured at 450 mV) increased to 3.40 mg/g, which was 73% higher than the capacity of the non-activated, raw electrode, and 5.76 times the adsorption capacity of the raw electrode at 0 mV. The results of this study indicate that air plasma activation can be used to effectively enhance the electrosorption capacity of carbon nanotube electrodes.