By 'context' we generally mean enough information to enable us to see what the word means. In your case, providing the sentence or two immediately preceding 'Something is off' should work.
I stared at him, speculating. He didn't seem to notice. His face was serene as he gazed out the windshield. Something was off, but I coudn't put my finger on it.
I hope this enables you to understand the context. Thanks.