KM3NeT/ORCA is a water Cherenkov neutrino telescope under construction in the Mediterranean sea. With ORCA, the KM3NeT collaboration will measure atmospheric neutrino oscillations to determine the neutrino mass ordering and constrain the oscillation parameters $\Delta m^2_{31}$ and $\theta_{23}$. In addition, Beyond the Standard Model hypotheses can be tested. In this contribution, the first ORCA measurement of the magnitude of the active-sterile mixing parameters $U_{\mu 4}$ and $U_{\tau 4}$ is presented. Using a dataset obtained with a very partial configuration of only $5\%$ of the final detector, with an exposure of 433 kton-year, ORCA is able to constrain simultaneously the two mixing elements under the hypothesis of an eV-scale sterile neutrino. The obtained limits are the second world's best limits on $|U_{\tau 4}|^2$.