Let \(q=p^\alpha \) for a prime \(p\ge 3\) and a positive integer \(\alpha \) , let \(\mathbb Z_q^*\) be a reduced residue system modulo q, k be an integer with \( k \mid \phi (q)\) . The purpose of this paper is to give an asymptotic property for \(N_{k}(n, q)\) , the number of representations of any element \(n\in \mathbb Z_q^*\) as sum of a primitive root and a k-th residue in \(\mathbb Z_q^*\) . In addition, we consider the square mean value of the error term of \(N_{2}(n, p)\) in this short note.