Your garage door opening on its own is more than annoying, it is a security risk. Here's what's probably causing it and how to fix it.
Radio frequency interference: Nearby devices (a neighbor's opener, ham radio) can sometimes trigger yours. Reprogram your opener to a new frequency or code.
Stuck wall button: The wired button inside your garage can stick or short out. Inspect the button and its wiring for damage or corrosion.
Faulty remote: A remote with stuck buttons can send signals without you knowing. Remove batteries from remotes you don't use.
Opener circuit board issues: Power surges can damage the board. A surge protector for your opener is a good investment.
Wiring short: Damaged wires from the opener to the wall button can cause phantom openings. Inspect for nicks or bare spots.
If reprogramming and checking buttons doesn't solve it, the opener likely needs professional attention.