git rebase has found a .git/rebase-apply directory and so presumes that you might be in the middle of a rebase. This would have happened if there was a conflict during a previous rebase and the rebase was not finished; i.e. you did not run one of git rebase --abort, git rebase --skip or git rebase --continue (the last one after resolving the conflict).

Solution by Siddhartha Reddy