When looking at IMDb only, there are many hints that it was dubbed.
First of all, the list of releases as also mentioned in santu47's answer lists an entry
USA 6 August 1999 (limited) (dubbed version)
So there seems to have been a dubbed English version, even if that was not the only version released in the US, seeing that the list also has entries for other releases (including non-festival releases that don't mention a dubbing):
USA 22 October 1998 (AFI Film Festival)
USA 23 October 1998 (limited)
USA 12 February 1999
UK 12 February 1999
The dubbed version was also not the version considered for the Academy Awards that the movie won, since IMDb's trivia section says:
Roberto Benigni's Oscar win for Best Actor was the second time a performance completely in Italian had been awarded.
Furthermore, it also says that
Horst Buchholz did his own dubbing for the English and German dubbed versions.
Which again references an existing English dubbed version. But the explicit mention of Horst Buchholz doing his own dubbing seems to suggest that this was not the case for all the other actors, though that is entirely specualtive deduction.
When digging a bit further I found various articles clearly mentioning a dubbed version of the movie that the studio Miramax released (with mixed responses, though) after the subtitled version already ran in US cinemas (which would be in line with IMDb's release list). This dubbed version was completely supervised by Roberto Benigni, since
Reaching a wider audience has always been a priority for him.
Yet Benigni for one didn't do his dubbing himself, but had it done by the American actor Jonathan Nichols, likewise with the role of Guido's wife Dora, who was voiced by Italian actress Ilaria Borrelli, and thus most probably with most of the rest of the cast.