The changes in the radical concentration and the development of the porous structure of the activated carbon obtained by pyrolysis in the presence of water vapor of various agricultural by-products are investigated by EPR spectroscopy and argon thermal desorption. It was found that they depend on the nature of the raw material and the final temperature of the process. A similarity was established between the dynamics of the change in radical concentration and the development of new surfaces of some of the activated carbons.