Taylor Swift made a surprise appearance at a local L.A. gastropub to celebrate someone's bday -- hanging out with a bunch of mere mortals without her boyfriend, Travis Kelce.

TMZ obtained these photos and videos of Taylor's West Hollywood outing Thursday night.

Check it out ... Taylor and one of her buddies rolled into Barney's Beanery, joining about 7 other people in a booth near the windows.

We're told Taylor was sitting with a bunch of older folks as well as some younger people – while trying to keep a low profile.

But that's impossible when you're an international pop superstar in a public place so everyone obviously recognized Taylor, yet no one came up and bugged her.

From what we saw, Taylor was just having a good ol' time at the table, chatting with her friends and eating some grub.

Meanwhile, Taylor's bodyguards were not stationed inside the joint, but they were outside keeping their eyes peeled for any trouble.

Our sources tell us ... Taylor spent about two hours at the soiree before saying happy birthday to one attendee, sliding out of the booth and leaving the restaurant.

Shortly after her exit, one of Taylor's bodyguards came into the bar and paid the tab for the group.