The contact problem of a rough, rigid surface with an elastic or viscoelastic incompressible semi-infinite body is studied in this paper. The problem is solved using a Boundary Element Method coupled with a conjugate gradient method. Viscoelasticity is taken into account with a 'State Variable' approach, making it possible to tackle the transient problem efficiently. The results are compared against Persson's theory of transient viscoelastic contact, showing good agreement in terms of contact area ratio and friction coefficient.