While Ronald's answer provides the correct date in a manner more acceptable to atheists or those of other religions, BC is nevertheless a more correct translation of ACN:

"Ante Christum Natum (du latin signifiant Avant la naissance de Jésus Christ), habituellement abrégé en A.C.N., a.C.n., a.Ch.n. ou ACN, exprime les années précédent la naissance de Jesus Christ[1]. C’est l’équivalent latin pour l'expression « av. J.-C. » (avant Jésus-Christ).

http://fr.wikipedia.org/wiki/Ante_Christum_Natum

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Note added at 47 mins (2012-07-18 13:18:35 GMT)
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Perhaps the question should be re-classified "Latin -> English"...

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Note added at 22 hrs (2012-07-19 11:10:41 GMT)
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While the distinction between BC and BCE might appear to be nitpicking, it could be important depending on context. While I have no idea what document you are working on or who the author is, it is conceivable that emphasis on the religious aspect of the dating system by choosing this less commonly-used form was actually deliberate.

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Note added at 1 day3 hrs (2012-07-19 16:04:25 GMT)
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I see what you mean about the baffling date. See the following from Wikipedia, for example:

Prior to 1066
Observation of Halley's Comet, recorded in cuneiform on a clay tablet between 22 and 28 September 164 BCE, Babylon, Iraq. British Museum. Halley may have been recorded as early as 467 BCE but this is uncertain. A comet was recorded in ancient Greece between 468 and 466 BCE; its timing, location, duration, and associated meteor shower all suggest it was Halley.[51] According to Pliny the Elder, that same year a meteorite fell in the town of Aegospotami, in Thrace. He described it as brown in colour and the size of a wagon load.[52] Chinese chroniclers also mention a comet in that year.[53]

The first certain appearance of Halley's Comet in the historical record is a description from 240 BCE, in the Chinese chronicle Records of the Grand Historian or Shiji, which describes a comet that appeared in the east and moved north.[54] The only surviving record of the 164 BCE apparition is found on two fragmentary Babylonian tablets, now owned by the British Museum.[54]

http://en.wikipedia.org/wiki/Halley's_Comet