We present the results of muon-spin relaxation measurements on ferromagneticBiMnO3.Below TC = 98.0(1) K oscillations in the time dependence of the muon polarization are observed, characteristicof a quasistatic magnetic field at a single muon site, allowing us to probe thecritical behaviour associated with the magnetic phase transition. We are able tosuggest candidate muon sites on the basis of dipole field calculations. Close toTC, fluctuationsof the Mn3+ moments are characteristic of critical behaviour while there is a sharp crossover to a regionof fast dynamic fluctuations at higher temperatures.