You should always be concerned about garage door cables fraying especially when consideration is made that the problem is only likely to get worse. We would advise against any use of the garage door if it appears that your garage door could compromise your personal safety. Most garage doors operate through the use of heavy-duty springs which enable the easy open/close operation of your garage door. The sudden break of a cable could cause a spring to suddenly lose tension and/or snap causing incidental injury. If the cable is severely frayed to where there is only a few strands left that could break at any moment, the cable should be replaced by a qualified garage door service technician as soon as possible.