Puerto Vallarta is a popular Pacific coast destination for foreign tourists. It was not known if any foreign tourists were among the approximately 100 people in the bar when the attack occurred.
Mariana Sanchez, Al Jazeera's Latin America correspondent, said there were differing reports about what happened.
"We are hearing that gunmen entered the bar and threw a grenade on the table. The other version is that someone was playing with the grenade when it went off," she said.
"There are no dead [people] but the victims are seriously wounded."
Violence in Jalisco has increased since security forces killed in July a prominent drug trafficker, Ignacio "Nacho" Coronel, who controlled the drug trade in the state.
More than 28,000 people have died in escalating drug violence since Felipe Calderon, the Mexican president, launched his war on drugs in late 2006, but tourists are almost never targeted.
The Puerto Vallarta attack came a day after the discovery of the bodies of 72 people thought to be migrant workers in an empty building on a remote ranch in northern Mexico.