In this paper we present the numerical analysis of the quasi-static behavior of an unbalance cracked shaft with straight and elliptical cracks considering an eccentric mass. The rotation of the shaft has been simulated by considering different angular positions to complete one rotation. The influence of the mass eccentricity in the opening of the crack has been studied considering different angles of eccentricity. The study of the partially opening/closing of the crack in the rotation of the shaft under the influence of the eccentric mass is analyzed. The work allows us to know the influence of the unbalance in the crack breathing mechanism and will help to predict the influence of this behavior on the values of the Stress Intensity Factor and on the propagation of cracks.