Under Penal Code Section 851.91, a person who has suffered an arrest that did not result in a conviction may petition to the court to have his or her arrest and related records sealed.
In other words, if you were arrested and your arrest did not result in a conviction, you may qualify to have your arrest sealed. Some examples of this include being arrested with no subsequent charges filed by the prosecuting agency and having your prior conviction vacated under Penal Code section 1473.7 followed by a dismissal under either Penal Code section 1382 or 1385.
It is important to note that although the prosecuting agency may not have filed charges against you, the prosecuting agency typically has a one (1) year Statute of Limitation for misdemeanor offenses and three (3) years for most felony matters to file charges. Each circumstance is unique so it is best to consult an experienced criminal defense attorney to evaluate your matter.