Context. Determining the metal content of low-mass members of young associations provides a tool that addresses different issues, such as triggered star formation or the link between the metal-rich nature of planet-host stars and the early phases of planet formation. The Orion complex is a well known example of possible triggered star formation and is known to host a rich variety of proto-planetary disks around its low-mass stars. Available metallicity measurements yield discrepant results. Aims. We analyzed FLAMES/UVES and Giraffe spectra of low-mass members of three groups/clusters belonging to the Orion association. Our goal is the homogeneous determination of the metallicity of the sample stars, which allows us to look for [Fe/H] differences between the three regions and for the possible presence of metal-rich stars. Methods. Nine members of the ONC and one star each in the λ Ori cluster and OB1b subgroup were analyzed. After the veiling determination, we retrieved the metallicity by means of equivalent widths and/or spectral synthesis using MOOG. Results. We obtain an average metallicity for the ONC [Fe/H] =-0.01 ± 0.04. No metal-rich stars were detected and the dispersion within our sample is consistent with measurement uncertainties. The metallicity of the λ Ori member is also solar, while the OB1b star has an [Fe/H] significantly below the ONC average. If confirmed by additional [Fe/H] determinations in the OB1b subgroup, this result would support the triggered star formation and the self-enrichment scenario for the Orion complex.