  We study the host properties and environment of active galactic nuclei (AGNs)
galaxies, taken from SDSS-DR12, across the $\text{[O III]}/\text{H}\beta$ vs
$\text{[N II]}/\text{H}\alpha$ diagnostic diagram. We select AGN subsamples
defined as parallel and perpendicular to the star-forming locus on the BPT
diagram based on the Kauffmann et al. and Schawinski et al. criteria. For
parallel subsamples we find that AGN host properties exhibit a morphological
evolution as they become more distant to the star-forming sequence. The local
density environment shows a more evident morphology-density relationship for
subsamples mainly formed by Composite and Spiral galaxies than those containing
LINERs and Seyferts, where the AGN emission is the dominant source. We also
analyse the properties of the five closest AGN neighbours observing no
significant differences in the environment, although the AGN host properties of
every subsample have noticeable variations. The AGNs belonging to perpendicular
subsamples show clear differences on their host properties from left top to
right bottom on the diagram. However, the analysis of the local density
environment do not reflect strong dependency with the host AGN properties. This
result is reinforced by the characteristics of the AGN neighbouring galaxies.
These findings suggest that mixed AGN/star-forming galaxies present
environmental features more similar to that of non-active galaxies. However, as
AGNs at the centre of the more evolved galaxies become the dominant source, the
environment tends to provide suitable conditions for the central black hole
feeding with an increasing content of gas and likelihood of a higher merger
rate.
