This is a continuation negative-muon spin rotation and relaxation (mu-SR) experiment on MgB2 having a superconducting transition at 39 K. Since positive muons start to diffuse in MgB2 even at 12.5 K, it is very difficult to study a change of the internal magnetic field in MgB2 across Tc with mu+SR. On the other hand, we found that the mu-SR spectrum clearly shows a static behavior even at room temperature. Therefore, we need to measure the mu-SR spectra of MgB2 at low temperatures for clarifying the change in the internal magnetic field accompanied with the superconducting transition.