The 'Starships' star, dressed in a PVC corset with large platform heels, was greeted by 500 fans at the event, held in Bayswater, London.
Minaj, who arrived in London on Wednesday to scenes of chaos at Heathrow, signed copies of her number one album Pink Friday: Roman Reloaded.
The 29-year-old has also filmed an interview with BBC One chatshow host Graham Norton, which airs tonight at 10.35pm.
Speaking to Norton, Minaj admitted that she had been taken aback by her Superbowl kiss with Madonna earlier this year.
"You can't really call it making out. She kissed me but I didn't kiss her," she said. "I wasn't expecting it and was shocked like everyone else. I was shaking and thinking, 'Is this really happening and why is she doing this?'"
She added: "It was the strangest thing, except she had very soft lips... I guess you could say that [she's a good kisser], but we didn't hang around in that lip-locking thing. It wasn't all drawn out and crazy."
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