The comedy in Pride and Prejudice comes from observing the behavior of particular characters, characters whose behavior rings so true to life that their actions have a comic tone. Two such characters, for me, are Mrs. Bennet and Mr. Collins.
Both Mrs, Bennet and Mr. Collins are very earnest. It isn't their intention to be "funny." Nevertheless, Mrs. Bennet's constant worry over to whom she and Mr. Bennet will marry their daughters, and the way she exclaims over every "high-born" person she meets, is funny. For Mr. Collins (whose constant reference to "The Lady Catherine de Bourgh" belies a social climbing heart close to Mrs. Bennet's beneath his clergyman's frock) the humor of his character is found in the incongruity between his role in life (clergyman) and his actions (social climbing).
Both of these characters are also perfect foils, which increases their comic value. Mrs. Bennet wouldn't be nearly so funny without Mr. Bennet's dry responses to her words of worry. And Mr. Collins' "suck-up" nature blooms more humorously in the presence of Lady de Bourgh.
Comedy is definitely present in Pride and Prejudice, but it must be found in the details of character behaviour, especially the behaviour of Mrs. Bennet and Mr. Collins.
For more on the irony and wit found in Pride and Prejudice, please follow the link on "humor" below.