In this work we present the results of the spectroscopic analysis in the near-infrared J band of a sample of 48 star forming galaxies at z = 0.84. Half of the sample was selected by a narrow-band filter tuned to Hα at that redshift and the other half was selected by photometric redshifts at the same redshift. We provide Hα luminosities and star formation rates for all galaxies at that redshift. We were able to estimate metallicities from [NII]6584 Å for a sub sample of eight galaxies, two of the galaxies were from neckband selection. To analyze their physical properties we have computed their sizes, colors, stellar masses, extinctions and other parameters available in literature and in the Rainbow database. In particular the dependence of the stellar mass with the specific star formation rate and metallicity have been studied and compared with the results of other samples of galaxies at several redshifts. For a fixed mass, the metallicities of our galaxies are compatible than those similar at the local Universe, although with higher dispersion. This fact implies that selection in Hα is less biased than a selection in UV, since it includes galaxies with more evolved populations besides objects dominated by star formation. The comparison of the observed properties with models of evolution leads us to think that z = 0.8 star-forming galaxies have already undergone significant changes and begin to developed in a more passive way.