I have a bit of experience with liquor laws here in Texas (20 years or so) and there is good advice in the above posts, but what it boils down to is this.
Is the beer free, or are you charging for it.
While every state has it's own laws, here in Texas, if you are giving the product away, you do not need a temporary serving permit from the TABC, nor do you need to have servers or bartenders that are TABC certified.
The TABC cannot prevent you from giving away beer or wine, since you have already paid tax on it at the store, and you are not making a profit. Now since this is homebrew, you have not paid TABC tax on it, but they would not know that.
The way that folks get into trouble is by asking for donations, asking that a cover charge is paid, or that you have to buy a cup. At that point, money is being exchanged, and you need a license for it. Some are cheap, you can get a weekend permit here for a $200 administrative fee, and a $30 charge for the license itself.
If it is free, they can't do a thing about it. Unless you are serving minors. Again, your state may be different, but at least around here, as long as you take zero money for what you are giving out, you are in the clear.