The Submarine star will reprise his role as vampire Adam on the paranormal drama this Sunday.
"Adam's just an excuse for me to f**k around," he told SFX. "Not that I don't like the script, which is awesome, but it's cool that you get freedom [with the lines].
"I think they trust that I won't be too ridiculous with it... although I have been too ridiculous with it in this episode! It's ridiculous. It's the end of my career."
Roberts also revealed that he would be happy to return to Being Human for a third time.
"They left it open again - they haven't killed [Adam] off, so I could be coming back, any time I want," he suggested. "I could come back and I probably would - it's just a laugh.
"The crew are cool, the cast are cool and like I said, you get freedom - you don't have to stick to the lines. Even though the lines are good and it's a really well-written show."
Being Human continues on Sundays at 9pm on BBC Three. In the US, the new series airs on Saturdays at 9/8c on BBC America.
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Watch a trailer for Being Human below: