We present the analysis of a sample of Halpha, Hbeta and [OII] emission line galaxies from the OTELO survey, with masses typically below log(M*/Msun) = 9.4 and redshifts between 0.4<z<1.43. We study the star formation rate, star formation rate density, and number density and their evolution with redshift. We obtain a robust estimate of the specific star formation rate - stellar mass relation based on the lowest mass sample published so far. We also determine a flat trend of the star formation rate density and number density with redshift. Our results suggest a scenario of no evolution of the number density of galaxies, regardless of their masses, up to redshift z=1.4. This implies a gradual change of the relative importance of the star forming processes, from high-mass galaxies to low-mass galaxies, with decreasing redshift. We also find little or no variation of the star formation rate density in the redshift range of 0.4<z<1.43.