Lostfocus event to be fired only on tab click from keyboard

I have a textbox  with lost focus event(integration triggers(mvvm)) to call some method and button to clear the textbox.I want event to fire on lost focus(i.e on tab click from keyboard).My issue is I have  entered text in textbox and tried to clear clear the textbox by clicking clear button actually lost focus event is firing before clearing the fields which is creating problem. I don't want lost focus to fire on click on button .