The OPERA experiment searching for nu(mu)- nu(tau) oscillations in the CERN to Gran Sasso nu(mu) beam, has detected so far three candidates of nu(tau) charged current interactions. All three events are attributed by the authors to the standard nu(mu)-nu(tau) oscillation at the atmospheric $Dm^2$. It is then possible to constrain the number of additional interactions, which could e.g. result from non-standard oscillations involving more than 3 neutrino mass states. In this paper, a 90 percent CL upper limit of 5.5 events is set on the number of additional nu(tau) interactions. This limit is then converted into limits on exotic nu(mu)-nu(tau) oscillations.