CBET 4929 & MPEC 2021-C16, issued on 2021, February 04, announce the discovery of a comet (magnitude ~19) in infrared images obtained during Jan. 22 UT with the Near-Earth Object Wide-field Infrared Survey Explorer (or NEOWISE; formerly the WISE earth-orbiting satellite). The new comet has been designated C/2021 B3 (NEOWISE). We performed follow-up measurements of this object while it was still on the PCCP webpage. Stacking of 50 unfiltered exposures, 30 seconds each, obtained remotely on 2021, January 27.1 from X02 (Telescope Live, Chile) through a 0.6-m f/6.5 astrograph + CCD, shows that this object is a comet with a compact coma about 10" arcsecond in diameter. (Observers E. Guido, M. Rocchetto, E. Bryssinck, M. Fulle, G. Milani, C. Nassef, G. Savini, A. Valvasori).