Let U be the open unit disk
in the complex plane and f a function defined on U. We show that if A is an infinite
dimensional dual B∗-algebra, then f defines a ∗-action in A if and only if f is
continuous at zero and f(0) = 0. We also obtain that if A is commutative, then f
defines a continuous action in A if and only if f is continuous on U and
f(0) = 0.