  We examine the properties of the host galaxies of 22,623 narrow-line AGN with
0.02<z<0.3 selected from a complete sample of 122,808 galaxies from the Sloan
Digital Sky Survey. We focus on the luminosity of the [OIII]$\lambda$5007
emission line as a tracer of the strength of activity in the nucleus. We study
how AGN host properties compare to those of normal galaxies and how they depend
on L[OIII]. We find that AGN of all luminosities reside almost exclusively in
massive galaxies and have distributions of sizes, stellar surface mass
densities and concentrations that are similar to those of ordinary early-type
galaxies in our sample. The host galaxies of low-luminosity AGN have stellar
populations similar to normal early-types. The hosts of high- luminosity AGN
have much younger mean stellar ages. The young stars are not preferentially
located near the nucleus of the galaxy, but are spread out over scales of at
least several kiloparsecs. A significant fraction of high- luminosity AGN have
strong H$\delta$ absorption-line equivalent widths, indicating that they
experienced a burst of star formation in the recent past. We have also examined
the stellar populations of the host galaxies of a sample of broad-line AGN. We
conclude that there is no significant difference in stellar content between
type 2 Seyfert hosts and QSOs with the same [OIII] luminosity and redshift.
This establishes that a young stellar population is a general property of AGN
with high [OIII] luminosities.
