A crowd of over 3,000 young girls and their parents showed up at the event, and things got out of control.
Bieber's manager Scott "Scooter" Braun was arrested after officials said they asked him to tweet that the event was cancelled, but they say he refused.
Scooter was charged with reckless endangerment and criminal nuisance.
The case is significant because it shows how a social media network can be misused and put individuals at risk.
As part of the deal, Bieber will record a videotape about the dangers of cyber-bullying and sexting that will be played at every school in Nassau County.
Bieber's record label also agreed to reimburse Nassau County for almost $8,000 to help pay its share of expenses for the large number of law enforcement officials that tended to the crowds.