The actor, who left for a birthday getaway with Malaika Arora two days before the special day, is son of film producer Boney Kapoor.
Arjun worked as assistant director and associate producer in several films, including the 2003 drama "Kal Ho Naa Ho" and "Wanted". He made his Bollywood debut with "Ishaqzaade" in 2012.
He was later seen in films such as "Gunday", "2 States", "Ki & Ka", "Finding Fanny", "Aurangzeb" and "India's Most Wanted". He is currently prepping for his next film "Panipat", a historical drama.
On his birthday, his sister Anshula posted his childhood picture, and wrote: "I don't really understand what this pose is, but I do know that there's no one else I would rather be my weird self with."
Here's what others posted on social media:
Anil Kapoor: Happy Birthday chachu Arjun. You make us so happy everyday! Always giving your 100 per cent to everything! You're all heart! I hope you keep rising higher and overcome every obstacle and reach the success you deserve! Love you!
Sonam Kapoor: Happy Birthday Arjun! Whether we're flash dancing on the streets or chasing slopes, it's never a dull moment. You bring so much laughter and weirdness to my life, and all those around you that we really wouldn't have it any other way. I wish you the best birthday, and all my love.
Ayushmann Khurrana: Happy bday fellow AK Arjun Kapoor! Have a good holiday.
Farah Khan: Happiest birthday Arjun Kapoor. So proud of your journey. From when you gatecrashed my sangeet to now. Love you more than you think. (P.S. He was invited by the way).
Kriti Sanon: Happy birthday Arjun! One of the most entertaining co-stars I've had. Stay the amazingly warm and genuine person you are! Wish you all the happiness, lots of love and everything that you dream of!
Guru Randhawa: Wishing my bro Arjun Kapoor a very happy birthday. Love you bro.
Kubbra Sait: Happy birthday Arjun.
Divya Dutta: Happy bday Arjun. Lots of love and happiness.
Maniesh Paul: Happy birthday Arjun! stay blessed bro...keep shining
Patralekhaa: Happy Birthday Arjun. Have a good one.
Anup Jalota: 'Hua chokra jawan rey'! Happy Birthday Arjun Have a great year ahead, God bless you with loads of happiness and success.
( With inputs from IANS )