  We study the star formation rate and dust extinction properties of a sample
of nearby star forming galaxies as derived from Halpha and UV (2000 A)
observations and we compare them to those of a sample of starburst galaxies.
The dust extinction in Halpha is estimated from the Balmer decrement and the
extinction in UV using the FIR to UV flux ratio or the attenuation law for
starburst galaxies of Calzetti et al. The Halpha and UV emissions are strongly
correlated with a very low scatter for the star forming objects and with a much
higher scatter for the starburst galaxies. The Halpha to UV flux ratio is found
larger by a factor ~ 2 for the starburst galaxies. We compare both samples with
a purely UV selected sample of galaxies and we conclude that the mean Halpha
and UV properties of nearby star forming galaxies are more representative of UV
selected galaxies than starburst galaxies.
  We emphasize that the Halpha to UV flux ratio is strongly dependent on the
dust extinction: the positive correlation found between F{Halpha}/F{UV}$ and
F{FIR}/F{UV} vanishes when the Halpha and UV flux are corrected for dust
extinction. The Halpha to UV flux ratios converted into star formation rate and
combined with the Balmer decrement measurements are tentatively used to
estimate the dust extinction in UV.
