Is it safe to eat marinated beef that has been frozen for three days?
As far as safety goes, you're fine, assuming the meat didn't stay unfrozen for too long before you refroze it.

As far as the efficacy of the marinading process, I'd think that the freezing/freezer burning process would go a long way toward preventing the marinade from imparting a lot of flavour and/or tenderness. Still, 3 days frozen is nothing. Shouldn't hurt anything.