The slowly pulsating B3V star 16 Pegasi was discovered by Hubrig et al.\ (2006) to be magnetic, based on low-resolution spectro-polarimetric observations with FORS at the VLT. More than 50 years ago it was reported to show emission in H$\alpha$, giving the star its Be status, although this emission phase was never confirmed. So far no confirmed magnetic field has been reported for a Be star. We have confirmed this discovery with high-resolution spectropolarimetry obtained with Narval at the TBL, France in 2007. We searched for rotational modulation of the field, and also for stellar wind variations in archival IUE spectra. We found a varying magnetic field, the largest measured strength of the longitudinal field being about 170 $\pm$ 45 G. The time resolution was not sufficient to establish the rotation period, which is estimated to be about 1.6 d. During our observations H$\alpha$ did not show emission.