Mine too! Only from cold though. My vibration kicks in just under 70 and stays till about 80ish. I changed the badly worm from brake discs and the vibration has gone. Most likely a badly balanced wheel or really worn disc. The other possibility is an egged tyre, where it's gone out of shape a big egged! Pretty much only happens to dirt cheap foreign brands or after a heavy hit. Also, really unlikely possibility is really badly shot shock absorbers as they can bounce over certain road surfaces if the seals have gone.
I'd start with a good wheel balance. Go for sticky weights, not rim weights, while your at it get the fitter to look at the tyre and check for damage. My wife had a fiesta years ago that had an egged tyre after she hit a fence post that had dropped of a lorry in front. The tread looked fine, but a patch.in the middle of the tyre was buldging out.
2005 Focus C-Max 1.8 Petrol Ghia + Sony 6 disc, 2007 tail lights, Led bulbs all over and HID front fogs.