The incident occurred on on July 19, after 2:00 pm, when Military Police arrested a Russian citizen for "launching an unmanned aircraft" over the Ministry of Defense, a statement said.
An unmanned aerial vehicle operator was transferred to the State Police. He was not named.
New laws introduced on July 4 this year made it an offense to fly drones over military installations, including the Defense Ministry building itself, or within 50 meters of that particular building.
For other military installations such as bases, depots and firing ranges, the exclusion is extended to 500 meters.
According to LSM's Latvian language service, the arrested man told police he was unaware that he was flying over the Ministry of Defense and had wanted to obtain footage of the National Art Museum on the opposite side of the road and parts of Riga's art nouveau and Old Town districts.
The prohibitions were introduced after previous attempts by Russian citizens to disrupt NATO military exercises in Latvia and unconfirmed reports, not only in Latvia, that drones of unknown origin have often been seen in the air near military facilities and exercises including last year in Sweden and Norway.
Military exercises in Estonia have also seem unidentified drones in the air, with Kremlin propaganda channel RT even boasting that it had drone footage of 2016's Spring Storm exercises near Voru.