Posted on May 4, 2012
Base Attack Bonus (BAB): Each creature has a base attack bonus and it represents its skill in combat. As a character gains levels or Hit Dice, his base attack bonus improves. When a creature’s base attack bonus reaches +6, +11, or +16, he receives an additional attack in combat when he takes a full-attack action (which is one type of full-round action—see Combat).
The above text is from Common Terms under the Getting Started section of the Core Rule book. It would appear than Ben was correct about the extra attack at a BAB of +6.