{babes} Jessica Simpson's Ruby Engagement Ring!

FIRST LOOK: Jessica Simpson's Ruby Engagement Ring! | Jessica Simpson

Jessica Simpson showed off her brand new Neil Lane engagement ring at Dillard's department store in Kansas City on Saturday as she was promoting her clothing line.

Her boyfriend of five months, Eric Johnson, proposed to Simpson with a three-stone ring that features a central ruby flanked by two diamonds.

"She was in a really good mood," an eyewitness at the store tells PEOPLE. "She was very friendly and sweet. She signed autographs and seemed to have a great time."

Only a few weeks ago, the singer, 30, gushed about her beau, 31, to PEOPLE – but didn't want to "jinx" their relationship.

"He's the one for me right now!" she said. "I'm very happy! I'm in a great place, and if right now could last forever, I'd take it."