Kapoor, 64, worked with Khan in films like "Zamaane Ko Dikhana Hai", "Naseeb", "Hum Kisise Kum Nahi", "Chala Murari Hero Banne", "Naqab" and "Ginny Aur Johnny".
The veteran actor shared a sweet message for Khan on Twitter by posting his picture.
"Happy Birthday Big Bear Amjad Khan. Remembering you. Baby Bear," he wrote.
Khan is best known for his portrayal of Gabbar in Ramesh Sippy's "Sholay".
After the success of "Sholay", Khan continued to play negative roles in many subsequent Hindi films in the 1970s, 1980s and early 1990s. He worked in over 130 movies in a career spanning nearly twenty years.