Some possible reasons why a doorbell might ring on its own include interference if it's a wireless doorbell and moisture near the button, notes HeathCo. Wiring problems, on the other hand, are rarely a cause of doorbell ringing issues, states This Old House.
Wireless doorbells use security codes, and if a neighbor has the same kind of doorbell model and the same code, the doorbell might ring when the neighbor's doorbell is pushed. This interference can be fixed by changing the security code, notes HeathCo.
If the doorbell's push button has some kind of moisture inside it, it may cause a chime even when nobody pushes it. Fixing this involves letting the push button dry out and possibly using a sealant to prevent moisture from getting inside the button again.