  We have analyzed the clustering of ~ 90,000 narrow-line AGN drawn from the
Data Release 4 (DR4) of the SDSS. We compute the cross-correlation between AGN
and a reference sample of galaxies, and compare this to results for control
samples of inactive galaxies matched simultaneously in redshift,stellar
mass,concentration, velocity dispersion and the 4000A break strength. We also
compare near-neighbour counts around AGN and around the control galaxies. On
scales larger than a few Mpc, AGN have almost the same clustering amplitude as
the control sample. This demonstrates that AGN host galaxies and inactive
galaxies populate dark matter halos of similar mass.On scales between 100kpc
and 1Mpc,AGN are clustered more weakly than the control galaxies. We use mock
catalogues constructed from high-resolution N-body simulations to interpret
this anti-bias, showing that the observed effect is easily understood if AGN
are preferentially located at the centres of their dark matter halos. On scales
less than 70 kpc, AGN cluster marginally more strongly than the control sample,
but the effect is weak. When compared to the control sample, we find that only
one in a hundred AGN has an extra neighbour within a radius of 70 kpc. This
excess increases as a function of the accretion rate onto the black hole, but
it does not rise above the few percent level. Although interactions between
galaxies may be responsible for triggering nuclear activity in a minority of
nearby AGN, some other mechanism is required to explain the activity seen in
the majority of the objects in our sample. (abridged)
