William Roache has been arrested on suspicion of raping a 15-year-old girl in the 1960s.
A man, aged 81, from Wilmslow, Cheshire, is being questioned at a Lancashire Police station, police said.
The offences are alleged to have been committed in Haslingden between April and July 1967, officers said.
Neither William Roache, who has played Ken Barlow in Coronation Street since 1960, nor his representatives have commented.
A Coronation Street spokesman said: “Given that a police investigation is under way it would not be appropriate to comment.”
A spokesman for Lancashire Police said: “An 81-year-old man from Wilmslow in Cheshire has this morning, Wednesday May 1 2013, been arrested by Lancashire Constabulary on suspicion of rape.
“The man will be interviewed at a police station in Lancashire during the course of the day.
“We take all allegations of sexual abuse extremely seriously and would encourage people with any information about sexual abuse, or anyone who has been a victim of sexual abuse, to come forward and report their concerns confident in the knowledge they will be investigated appropriately and with sensitivity.”
Two police officers are stationed by the closed wrought iron gates outside the star’s home.
In March William Roache issued an apology after he appeared to suggest in a New Zealand television interview that sex abuse victims were being punished for behavior in “previous lives”.
The actor also said if there was anonymity for people making accusations of child sex offences, there should also be anonymity for those accused because of the stigma they faced even if innocent.
William Roache has an award from Guinness World Records for being the world’s longest-serving soap actor, having played Ken Barlow since Coronation Street’s first episode.