Jessica Alba thought it was "really cool" when a cop showed her his tattoo of his face.

Jessica Alba

Jessica Alba

The 'Sin City' actress - who has daughters Honor, eight, and five-year-old Haven with husband Cash Warren - feared the worst when a patrol car stopped outside a house where she was showing her "drunk mom" friends her new car, but was stunned when the "nervous" officer revealed his real reason for pulling over.

She told talk show host Jimmy Kimmel: "On the weekends my friends and I, we hang out and sometimes we day drink.

"We're the white wine with ice in a cup, very sophisticated, because we don't want our kids to know we're drinking."

As they went outside to see the car, the patrol car pulled up.

Jessica added: "I was like, 'Oh no!' Like, we [have] alcohol. Are we going to get in trouble? 'This is not a good look -- a bunch of drunk moms in the middle of the day.

"But he was like, 'Oh no, I backed up because I wanted to show you that I have you on my arm!'

"He was totally bugged out, 'Is it you?' He got it in college, he couldn't talk, he was that nervous, and he was sweating.

"I was like, 'Can I see it?' And then he said yeah, but then he had to stop and take all [his gear] off."

The talk show host suggested other people might not have been so excited.

He asked: "And you find this flattering?"

Jessica replied: "I mean, yeah! It's pretty cool."

The 35-year-old actress shared a brief video of the encounter on Instagram a few days ago and admitted it was one of the "more surreal" moments of her life.

She wrote: "Definitely one of the more surreal moments of my life - This sweetie pie young officer drove by outside my friends house and stopped to tell me he had my face tattooed on his arm - of course I HAD to see it! So cool and such a trip.(sic)"