In this case, considering the attached picture wherein you can see the presence of the parent chain as aniline, we can see radicals at the nitrogen, named by N-ethyl and N-methyl which are the present alkyl substituents. In such a way, the benzene ring is not considered an alkyl radical because it belongs to the parent chain on aniline and therefore, N-ethyl-N-methylaniline has two alkyl substituents.