Is frequent a noun

No, the Word 'frequent' is a verb (frequent, frequents, frequenting, frequented) and an adjective (frequent, more frequent, most frequent).

Examples:

Sometimes we go to the big supermarket but we frequentthe store on our corner. (verb)

In the summer we make frequent trips to the beach. (adjective)

The noun forms of the verb to 'frequent' are frequency and the gerund, frequenting.

The noun form of the adjective 'frequent' is frequentness.