There was no immediate word on the motive of the shooting. Police said at least seven masked gunmen fired into the bar in the city of Belem.
Five women and six men, including the owner, were fatally wounded. Another man was injured in the attack. Several customers escaped injury by hiding in the back.
The bar, known as Wanda’s, was a well-known drug-dealing hangout. It came a day after five people were shot in the street by suspected gang members near the city of Salvador in the east of the country.