Just read the pk mug rules it explains lt pretty well.
But basically to answer your question no if you have your gun out on safety or in general before the person tries to initiate the mug it's considered a fail mug. However if you are already at gun point you risk yourself being pked as you're attempting to break the fearrp by fighting back. Also if they look away or stop pointing their guns at you, you can fight back without fear of being pked.