Sure - it's fairly common at startups, especially in urban areas where many or most people aren't driving home at night. If you like beer, it's a nice-enough perk.
Note that there's unwritten etiquette around the consumption of alcohol in the office - don't get sloppy or obnoxious, save it for lunch / the end of the day / Friday afternoon (varies from company to company), use common sense. No one arrives in the morning and helps themselves to a tasty pint during the morning stand-up.