The couple were seen browsing the selection in the Oxford Street branch of a High Street jeweller's on Valentine's Day.
Earlier this week co-star Anil Kapoor, claimed the pair are an item in real life as well as on the big screen.
Dev Patel and Freida Pinto, pictured at separate pre-Oscar parties in LA last night, play sweethearts in Slumdog Millionaire and are said to be dating off-screen too
Freida poses with Oscar nominee Kate Winslet at the US-Ireland Alliance pre-Academy Awards event in Los Angeles
An onlooker who saw the pair in H.Samuel's told The Sun: 'Dev and Frieda seemed completely smitten with each other. 'They spent 15 minutes in the jeweller's and were quite happy to sign autographs and talk to fans.
'They paid particular attention to one of the cabinets which was full of the more expensive rings stocked by the store chain.
'They didn't buy anything in the end, but they certainly spent plenty of time studying the range.'
The two young stars are said to have grown close while promoting the film - a favourite for the Oscars this weekend - around the world.
Indian actor Kapur said of the couple's relationship: 'I think this is the beginning of something exciting.
'They definitely make a great pair and look very good together.'
Patel, 18, from Harrow, has already bagged a clutch of awards for his role as Jamal in the film. Ex-model Pinto, 24, plays his sweetheart Latika.
Kapoor reportedly made his remarks on a U.S. radio station where he referred to their 'magical chemistry'.
Presenter Ryan Seacrest asked the actor: 'Dev and Freida...is there any action going on behind the scene there?'
While former Skins actor Dev gets to know actress Sienna Miller at the Grey Goose pre-Academy Awards party at Cecconi's in Hollywood
Anil Kapoor, who plays the Who Wants To Be A Millionaire host in the film, hinted the pair were dating after speaking about their 'magical chemistry'
Kapoor answered: 'As a matter of fact, when I meet them I feel there is something happening.'Patel first met Pinto during an audition for Slumdog Millionaire. Later she offered to take him around Mumbai and the two hit off very well.
The two debutantes are riding high on the unmatched success of their first gig.
After sweeping all major awards this season the duo now awaits the Oscars night on Sunday where the film has garnered whopping 10 nominations.
Not just on-screen lovers? Patel in a tender moment in a scene with Pinto, who plays Latika
Last night the pair were both in Los Angeles at separate pre-Oscar parties. Pinto looked stunning in a two-tone gold and yellow dress while Patel cut a dash in black trousers and a grey button-up top.According to friends, Pinto finished with her fiancé, Mumbai PR agent Rohan Antao, last month saying she could not be with him and be a world-renowned actress at the same time.
During her meteoric rise to stardom, she had kept Rohan a secret from the media.
Sources say that Rohan is 'devastated' at losing the girl he thought he was marrying.