Activated carbons were prepared from an original and demineralized subbituminous coal by a two-stage, pyrolysis and steam activation, treatment. The effect of demineralization, pyrolysis and steam activation processes on the evolution of the surface area, pore texture, and ζ potential has been investigated. The pyrolysis step increased the microporosity of the samples and decreased the negatively charged surface. The steam activation step increased the surface area and porosity as well as the surface basicity of the activated carbons. The electrokinetic behaviour of the carbons was affected by the presence of KNO3, because they specifically adsorbed either K− or NO3− ions depending on the sample. Finally, the demineralization process after the pyrolysis and steam activation was more effective than if the demineralization was carried out prior the two-stage treatment.