David Steinhof, a first-time candidate, joins two others in the Republican primary field, including Dr. Elizabeth Childs -- the state's mental health commissioner under Gov. Mitt Romney -- and Sean Bielat, The Boston Globe reported Thursday.
Joseph Kennedy III, Herb Robinson, Paul Heroux and Jules Levine have announced they will run in the Democratic primary.
Steinhof's campaign manager, Scott Anderson, said the dentist considers himself a "constitutional conservative, which could make him popular with the Tea Party movement, the newspaper said.
"His main concern is jobs," Anderson said.
Frank, 72, announced he would not run for re-election in November, a move he said was based partly on a redrawn district, with new constituents wary of an incumbent.