"The Queen is feeling well and is following her doctor's recommendations," it said.
She is almost asymptomatic, the Royal Palace added.
Mathilde, 49, who has been Queen of Belgium since 2013, has cancelled all her public events for the rest of this week.
Covid-19 hospitalizations in Belgium rose last month when the country removed almost all of its Covid-19 restrictions. However, the number seems to be declining again.
(Reporting by Charlotte Van Campenhout; Editing by Angus MacSwan)

Queen Mathilde of Belgium greets the MuCH Ensemble and the soloists of the Queen Elisabeth Music Chapel ahead the yearly Christmas Concert at the Royal Palace in Brussels, Belgium, 21 December 2021. EPA-EFE/PHILIPPE REYNAERTS / POOL