at the back of (one's) mind
Present in one's thoughts or in one's attention, without ever being fully obscured by any other thoughts or considerations. Whenever I park in the city, the fear of being towed is always at the back of my mind.
at the back of your mind
COMMON If something is at the back of your mind, you are aware of it, though it is not the main thing you are thinking about. It was not until they had eaten that Brigadier Ryle raised the subject that had been at the back of his mind throughout the meal. Always, at the back of my mind, was the fear that the depression might overcome me again.
at the back of your mind
not consciously or specifically thought of or remembered but still part of your general awareness.