The electron energy distribution function and the electron drift velocity a
re studied numerically in a decaying plasma in the external electric field
in the mixture Ar:F-2 = 1:0.005 at atmospheric pressure. For a reduced elec
tric field strength over the range 0.055-0.55 Td the negative electron mobi
lity was predicted earlier by the solution of the Boltzmann equation using
the two-term approximation for the velocity distribution function. The appl
icability of this approximation for calculations of negative mobility is di
scussed. The Monte Carlo simulation method is used to verify results obtain
ed from Boltzmann equation analysis. It is shown that there is a reasonable
agreement between the Boltzmann equation and Monte Carlo results.