Buhari said this during an interview aired on Arise TV which was monitored by our correspondent.
There have been growing demands for the IG, who has reached the retirement age of 60, to step aside.
However, there have been speculations that the President is considering extending his tenure till after the elections.
When asked his next line of action, Buhari burst into laughter, mocking those who had threatened to take action against him if he refused to sack Idris.
He, however, said he was not afraid of the IG and would take a decision soon.
The President said, “I don’t think I am afraid of him. And I don’t think I have asked him to mount roadblocks in place such that I’ll lose revenue (if he goes). But I’ll take action.”
Buhari, however, said removing service chiefs or the IG during a time of insecurity is a sensitive matter.