  We present preliminary results on the computation of the QCD running coupling
constant in the $\widetilde{MOM}$ scheme and Landau gauge with two flavours of
dynamical Wilson quarks. Gluon momenta range up to about 7 GeV ($\beta =$ 5.6,
5.8 and 6.0) with a constant dynamical-quark mass. This range already allows to
exhibit some evidence for a sizable $1/\mu^2$ correction to the asymptotic
behaviour, as in the quenched approximation, although a fit without power
corrections is still possible with a reasonable $\chi^2$. Following the
conclusions of our quenched study, we take into account $1/\mu^2$ correction to
the asymptotic behaviour. We find $\Lambda_{\rm \bar{MS}}^{N_f=2} = 264(27)
{\rm MeV} \times [{a^{-1}(5.6,0.1560)}/{2.19 {\rm GeV}}] $, which leads to
$\alpha_s(M_Z) = 0.113(3)(4)$. The latter result has to be taken as a
preliminary indication rather than a real prediction in view of the systematic
errors still to be controlled. Still, being two sigmas below the experimental
result makes it very encouraging.
