Let R be a ring with an automorphism φ of order two. We introduce the definition of φ-centrosymmetric matrices. Denote by Mn(R) the ring of all n×n matrices over R, and by Sn(φ,R) the set of all φ-centrosymmetric n×n matrices over R for any positive integer n. We show that Sn(φ,R)⊆Mn(R) is a separable Frobenius extension. If R is commutative, then Sn(φ,R) is a cellular algebra over the invariant subring Rφ of R.