We'd have to know what specific things your neighbor is actually doing. Penal Code Sec. 646.9, the stalking law, says: "Any person who willfully, maliciously, and repeatedly follows or willfully and maliciously harasses another person and who makes a credible threat with the intent to place that person in reasonable fear for his or her safety, or the safety of his or her immediate family, ..." is guilty of stalking, which can be either a felony or a misdemeanor.
Has your neighbor harassed you? More importantly, has he or she threatened you? If so, go to the police and report him or her.
Penal Code Sec. 646.91(a) says that a judge can issue an emergency protective (that is, restraining) order when a peace officer asserts reasonable grounds to believe that a person is in immediate and present danger of stalking -- that is, if you make a report, and the police officer believes you've been stalked. Subsection (b) says that the police officer himself can write and sign such an order.
If you seek and obtain such a restraining order, and if your neighbor continues his or her behavior, the consequences become more serious. Penal Code Sec. 646.9(b) says that someone who's convicted of stalking in violation of a court order or injunction SHALL (not "may") be punished by a two-, three- or four-year term in state prison.