USB Fuse to protect USB ports?
Note: this answer concerns marginal but far from comprehensively effective half-measures for protecting devices.  It does not address PERSONAL SAFETY in the slightest, because such was not part of the question at the time this was posted.

USB ports often (but not always) have thermally activated self-resetting fuses to protect against excessive current draw.  But that is only one type of electrical risk - it does nothing to protected the data lines for example.  

I believe there are full USB "isolators" (likely with optical coupling inside) but these are expensive for everyday use, so likely to be found only in industrial or test setups (for example, a programming pod used while developing motor controls).

Using a cheap sacrificial USB hub outboard of the computer may provide some degree of protection, though far from absolute as there is an electrical connection through the circuitry of the hub.