Mellor's Dr Matt Carter was tipped to begin a relationship with Keegan's Tina McIntyre earlier in the summer. However, the actress recently admitted that her character is conflicted between Matt and ladies' man Tommy Duckworth (Chris Fountain).
"When Chris and I are in character, we're like rutting stags trying to be the alpha male," Mellor told The Mirror. "Sometimes when the camera stops rolling, we carry that on in the green room and pretend we're competing over Tina.
"I'm sure there are a lot of jealous guys who wish they were in our shoes. Who wouldn't be? Most guys on the Street would like Tina as their on-screen girlfriend and I think, deep down, they all fancy Michelle.
"Everyone has a secret crush on her. But you can't really blame them, can you? There's a reason why Michelle is winning all these sexiest female awards. And she's lovely too. She doesn't have a bad bone in her body."
The 30-year-old continued: "When there's an on-screen romance you obviously have to get a bit closer physically, and you expect a bit of awkwardness. But there never was any with me and Michelle.
"We both like to have fun on set and when we did our first kissing scene I was joking all the day that I'd been eating crab paste and garlic to make my breath stink. She said she'd been eating something even worse. You have to joke about it."
Rating Keegan's kissing, Mellor said that she is "not as good" as his girlfriend Charlotte Bury. He also added that he has yet to meet Keegan's fiancé, The Wanted star Max George.
"I haven't met Max yet but there's really no reason why we wouldn't get on. She talks to me about him a lot, she's very excited about being engaged, and he's just a regular lad doing what he loves - their careers are storming. He's not a bad-looking lad either," he said.
"I don't think Charlotte was too thrilled with the fact my on-screen girlfriend was going to be Michelle Keegan but, let's face it, the doc was always going to get a love interest. As an actor that's what you hope for, so we had spoken about it beforehand, and now she's really pleased for me because it's like a promotion."
> 'Coronation Street' Michelle Keegan: 'Tina would feel out of place with Matt'
> 'Coronation Street' Michelle Keegan calls for Tina, David reunion Get the Inside Soap magazine on your iPhone or iPad