The forgotten topological index of a graph G is defined as the sum of the cube of the degrees of its vertices. In the recent paper [6], [W. Gao et al. (2016), Forgotten topological index of chemical structure in drugs, Saudi Pharmaceutical Journal, 24, 258-264], the forgotten topological index of some chemical structures has been obtained. In this note, we correct their result regarding triangular benzenoid. Also, we have given the expression for the forgotten topological index of graphene structure which is more compact than the one was obtained in the paper above.