The electromagnetic properties of the A-site-ordered perovskite manganite YBaMn 2 O 6 have been investigated by 55 Mn-NMR and μSR measurements. 55 Mn-NMR spectrum of YBaMn 2 O 6 at the ground state is consistent with a charge-ordered antiferromagnetic state, where eg-electrons of Mn3+ ions are well localized. In the antiferromagnetic state, three components of muon spin oscillation are observed in the μSR time spectra. The observed muon spin oscillating frequencies are consistently explained by the checker-board-type charge order and the antiferromagnetic spin order proposed by the previous neutron diffraction study. The most probable candidate for the muon site is near O(7) in the BaO plane of YBaMn 2 O 6 .