The woman involved is thought to have been McFadden's ex-girlfriend Angela Bostock.
Sky News crime correspondent Martin Brunt said the two incidents appeared to be unrelated.
But he added: "This will do no good for their tough-guy image."
Kemp and McFadden have just returned as the hardman Mitchell brothers, Grant and Phil, in the BBC 1 soap.
Rebeccah Wade, editor of The Sun, had been held in custody after police were called to her and Kemp's Battersea home at 4am this morning.
"Neighbours were woken by a disturbance of some description and decided to call the police," Sky News crime correspondent Martin Brunt said.
"The allegation is that Wade assaulted her husband. He is sporting a cut lip."
Brunt said that it has been claimed that Ms Wade had been out drinking with ex-Cabinet minister David Blunkett before returning home last night.
Brunt said her arrest "will be cause for some embarrassment. As editor, she has campaigned against domestic violence."
Kemp is thought to be carrying on his work at television studios after recently returning to the hit soap.
The couple have been together for some years and married in Las Vegas in 2002.
Ms Wade has been editor of The Sun for four years before which she edited The News of The World.
She had been due to attend the 50th Women of the Year Lunch this afternoon at the Guildhall in central London.
The Sun has not commented on the arrest.