  We estimate the quantity |f_eta'^(c)| which is associated with the charm
content of eta' meson from the experimentally known ratio R=B(psi ->eta' gamma
)/B(psi ->eta_c gamma). It is shown that due to the off-shellness of the c\bar
c component of eta', which has been overlooked so far, f_eta'^(c) is further
suppressed. Assuming that psi ->eta' gamma decay is dominated by psi ->eta_c
transition, we obtain |f_eta'^(c)| = 2.4 MeV which could imply that the (b ->
c\bar cs) mechanism does not play a major role in the B -> K eta' decay mode.
