Jessica Simpson and Eric Johnson Hang Out at Ashlee Simpson's Vegas Show

Jessica Simpson and Eric Johnson might have gone to Las Vegas together, but they're trying to keep a low profile while there ... though it wasn't easy for either of them to hide in a crowd at Jessica's sister Ashlee's show.

The two were spotted at Voltaire -- a popular nightclub in The Venetian Resort ... chatting with a group of people.

No PDA between the pair here ... but, they're clearly comfortable spending time with one another -- though video circulating online shows they put some distance between one another during Ashlee's actual performance.

Check it out -- Eric was nowhere near Jessica while Ash was singing ... but, eagle-eyed fans who search the crowd will notice he's standing just a little ways off -- wearing a Georgia Institute of Technology cap.

It's a bit hard to see his face in some of these snaps ... but, it's the same hat Eric was seen wearing when he and JS touched down in Sin City yesterday.

Remember ... the two were photographed flying from Burbank to Vegas yesterday -- with the pair touching down at Harry Reid International yesterday.

They were mum on reconciliation ... and, there's no PDA between the two in photos and videos from the concert -- but, it seems like another hint that these two might be trying to thaw their frosty relationship.

As you know ... Eric and Jessica announced their separation in January -- though our sources say they've been apart for much, much longer than that.