Coaster brake brakes itself My bike has a coaster brake (pedal brake). 

I am not sure how it started, but it has just started to brake itself even if I don't do back pedal. 

It works weirdly that, it is kind of latching the brake when I use the back pedal. Sometimes it gets fine especially when I do a strong pedal brake. But, it usually brakes itself and the strength of the brake varies, and time-to-time it gets fine itself for a while. It does not have a consistent state.

Does anyone have an idea what might be wrong with it and if it is something that I can fix it?

EDIT: Picture of the brake arm:
Are you sure that the friction comes from the hub, not from tyre rubbing against frame? Axle mounting point looks as it is not tightened properly.

Second thing to check is to assure that hub is not screwed too tight.

I would personally unscrew arm-side of the hub and check the clutch and its "spring" condition. It's easy, no special tools required. Check the very first minute of this video.