According to Emma Frost, yes.
But how the hell does she have one if she's from Boston? Many fans and characters have questioned the legitimacy of her claim and there are a couple theories to this.
She fakes it!
In "Astonishing X-Men: Xenogenesis" No. 4, Cyclops tells Storm that Emma has a fake English accent (and, no, the accent doesn't bother him). And that's that. Emma puts on a faux accent probably to reinforce her snobby, rich attitude. This wouldn't be out of character, though. She's had plastic surgery in the past, dyes her hair blonde, and wears those scantily clad outfits to give misleading presentations about her.
It's the real deal!
During the "Emma Frost" series, Astrid Bloom, Emma's telepathic acquaintance, taught Emma the basics of telepathy. Astrid hailed from England and had a strong English accent. She also used Emma's frequent terms of endearment such as dear and darling. Astrid's English roots were probably not a coincidence since the series was published after Morrison's "New X-Men," where Emma mentioned her English accent.
The bizarre but totally possible scenario is this: Astrid influenced Emma and gave her that accent when they were having their telepathic battle (in which Astrid died). Since Emma's power was not fully harnessed, it's possible that Astrid's accent transferred into Emma's mind and decided to keep it.
So does she?
Well, it's pretty ambiguous and debating would lead to more fanwank.
There is another possibility, though. Ms. Frost is telling the truth and nobody knows where the hell the accent came from. ;)