From Longman Dictionary of Contemporary Englishsomebody was (just) minding their own businesssomebody was (just) minding their own businessspoken used to say that someone was not doing anything unusual or wrong at the time when something unfair or bad happened to them I was driving along, minding my own business, when the police stopped my car. → business
Examples from the Corpus
somebody was (just) minding their own business• I was just walking along, minding my own business, when this guy ran straight into me. 