In April 2023, an outbreak of clade 2.3.4.4b highly pathogenic avian influenza A(H5N1) viruses carrying the T271A mammalian adaptive mutation in the PB2 protein was detected in a backyard poultry farm in Italy. Five domestic dogs and one cat living on the premises had seroconverted in the absence of clinical signs. Virological and serological monitoring of individuals exposed to the virus proved the absence of human transmission, however, asymptomatic influenza A(H5N1) infections in mammalian pets may have important public health implications.