In a typical young open cluster the polarimetric data shows, for normal stars, that the distribution of angles of the polarization vectors can be describe by a fixed value that caracterizes the cluster. Individual stars show some scatter over this mean angle because of fluctuations in the interstellar medium (ISM), variations in the magnetic field of the galaxy and the intrinsic polarimetric properties of the stars. NGC 6231 is one of the youngest open cluster in the Galaxy, locate in the Sco region. The distribution of its polarization angles is abnormal, and three diferent groups of stars can be determinated, according to the star location and to the angle of the polarization vectors. In particular, in the cluster's core, the vectors form part of a semi-circular structure, probably as a consequence of a energetic phenomena (supernova event) that has produced a shock over the ISM re-orienting the dust grains to the new direction of the magnetic field. In the present study, we discuss what probability there is that a supernova event could have happened in NGC 6231. We estimate the location and the age of the event and we study the relationship between the polarization and the extinction.