From Longman Dictionary of Contemporary Englishat/in the back of your mindat/in the back of your mindTHINK ABOUTa thought that is at the back of your mind is one you try to ignore because you do not want it to be true At the back of her mind was the thought that he might be with someone else.put/push something to the back of your mind He tried to push these uncomfortable thoughts to the back of his mind. → back
Examples from the Corpus
at/in the back of your mind• There was always a slight feeling of fear at the back of his mind.• I was hurt that she'd left, but I guess at the back of my mind I always knew she would.