if a grammar is regular then it will be Context free also [as per chomsky hierarchy] it may be or may be not ambiguous depending on grammar.
as
S->bS|aX
X->bS|aY
Y->aY|bY|^
is regular having regular expression (a+b)*aa(a+b)* and unambiguous
but grammar
S->aS|bS|aX
X->aY
Y->aY|bY|^
is also regular having regular expression (a+b)*aa(a+b)* and ambiguous.[check aaa]
But it is sure any ambiguous regular grammar can be converted into unambiguous regular grammar.