In my my(little) view both mean the same idea.
A :Can I borrow the book?
B: That's OK.(no problem)
Let's wait for our teachers' responses.Pronunciation: /əʊˈkeɪ/
used to express agreement or acceptance:
OK, I’ll pass on your message
OK, OK, I give in
used to introduce an utterance:
‘OK, let’s go’
Student or Learner