We present the first detection of the near-infrared CN absorption band in the nuclear spectra of active galactic nuclei ( AGN ) .
This feature is a recent star formation tracer , being particularly strong in carbon stars .
The equivalent width of the CN line correlates with that of the CO at 2.3 \mu m as expected in stellar populations ( SP ) with ages between \sim 0.2 and \sim 2 Gyr .
The presence of the 1.1 \mu m CN band in the spectra of the sources is taken as an unambiguous evidence of the presence of young/intermediate SP close to the central source of the AGN .
Near-infrared bands can be powerful age indicators for star formation connected to AGN , the understanding of which is crucial in the context of galaxy formation and AGN feedback .