A queen bee had attached herself to one of the posts, causing the penalty area to become a hive of activity.
The referee suspended the start of the friendly until some beekeepers arrived.
The club tweeted: "The Bee team has just left the pitch," while Blackburn's twitter feed read: "Un-BEE-lievable scenes here."
A club spokesman said: "We are very grateful to the local bee society who arranged for a beekeeper to come along and clear the bees."
Unfortunately for Oldham they also lost the game - 2-0