Why is my bedroom door moving if my windows are closed?

If a window somewhere else is open, it may very well affect your door, especially if its workings are loosened, or old. An open window somewhere in the kitchen or living room could do it, depending on how the apartment is laid out. Wedge a sock in the door, that should take care of that problem.

Unless it’s a ghost…

In an apartment building, there could be any number of other openings that would account for the wind movement. I agree with @Symbeline

I would guess a ghost.

Or an earthquake.

There may be airflow because the windows are not perfectly sealed, or the building might be swinging slightly in the wind.
But most likely, it is aliens.

In high winds, it’s not unusual to have a draft blowing around, even if your windows are closed. My windows even bang a bit in weather like that.

If you are on a high floor there could be a bit of sway in the building that you don’t feel, but could affect the door moving. Buildings move in high winds. There is a lot of thought put into dampening this affect, and at the same time allowing some sway for things like wind and earthquakes. If your air system is on, the air blowing through a vent could affect a door.

Normal flow of air, I suppose… or record the nightly door-activity with a webcam… well… if you see on that footage your friend/bf/gf standing for hours aside your bed… sell that to Hollywood. Just kidding. Sorry.

There’s probably a vent shaft or two in the apartment, in the bathroom &/or kitchen. The output of those, on the roof can easily see a pressure difference to the inside with a gust going by.

No building can be completely sealed (otherwise the inhabitants would eventually suffocate). It’s probably air vents or unsealed windows in other parts of the building. Light a candle and watch the flame; the direction of the flicker will show you which way the air is moving.

Yes, it is perfectly normal.

Your own apartment probably has several openings to the outside: kitchen range hood – if you have one – and bathroom fan vents, for example. Each of your plumbing fixtures (drains) is also vented, or they wouldn’t be able to drain properly. (Though this shouldn’t be affecting air movement in your apartment; the drain vents are isolated from you by the traps in the drain lines. People in single-family houses often notice their toilet bowl levels fluctuate and move – even sway! – during times of high wind, as the air moving over the top of the vent creates a temporary vacuum that sucks some of the water right out of the bowl.)

As others have also noted, the building itself is imperfectly sealed, and every time the entry door opens there’s a chance for a gust of wind to temporarily alter the air pressure throughout the entire common area.

Yep, a Ghost FTW!!!