1. inclined or likely to do something
To be 'of a mind' to do something
'I'm of a mind to' do something means to be inclined to or likely to do something, to literally 'make your mind up to do something' or to be thinking about it. This idiom is usually used as a threat to do something rather than actually take any action. It is an idiom you are more likely to hear colloquially in social situations.