is the sentence correct?

I'd say, it's not complete. Behind what?

Hi Paulio, the verb 'to leave' followed by 'behind' has got the meaning of 'forget', so you don't need to add something after behind. In fact the sentence that MyShirley posted is almost like: I forgot my keys in the office.
To my 'non-native speaker ears' MyShirley's sentence sounds correct, maybe some native speakers could confirm or correct me later

I left my keys behind in the office. (correct)

I left my keys in the office has the same meaning.

no

Oh, Francesca, many thanks for elucidation, I didn't know about
'leave behind' in the meaning of 'forget'. Then, the sentence is gramatically correct.