Caesars Windsor had a brief lockdown just before noon as part of an investigation by Windsor police.
Police spokesperson Sergeant Steve Betteridge says officers responded to the gaming facility to investigate a complaint.
One person claims to have been threatened by a person holding a weapon.
There is no injury associated with the incident and police are considering it an active investigation.
As a result they can't disclose what type of weapon was seen or provide a description of a suspect.
The lockdown was only done by the casino in the event the alleged suspect had entered the building.