Robert "Bob" Charles Frojen (December 1, 1930 – December 11, 2005) was an American water polo player of German descent who competed in the 1956 Summer Olympics.

Frojen was a member of the American water polo team which finished fifth in the 1956 tournament.

He played all six matches.

In 1981, he was inducted into the USA Water Polo Hall of Fame.

This biographical article relating to a water polo figure from the United States is a stub.