Muscle cars, pony cars, and affordable sports cars in general don't tend to have very great records for safety; but that's more due to the types of drivers they attract than to issues with the cars themselves.
The 2014 Ford Mustang is a pretty secure pick, if you plan to drive responsibly (and plan to get top-tier winter tires if you intend to drive it year-round).
In federal NCAP testing, the 2013 Mustang has earned four-star ratings overall, as well as for frontal and side impact. Mustang Convertible models have scored a top 'good' rating from the Insurance Institute for Highway Safety (IIHS) in frontal, side, and rear impact. Coupes earn 'acceptable' instead for side impact.
The safety-feature set is solid, too. Front and side airbags, anti-lock brakes, and stability control are included. Option the Mustang up with Bluetooth, blind-spot monitors, a rearview camera, and rear parking sensors, and you get more safety features than a number of mid-size sedans costing just as much.
The only catch? Outward visibility isn't great, particularly in Convertibles.