Local vendor said it is Aster, but I don't think so after Googling. What can it be?
It's a dianthus; its wide green leaves indicate that it's probably a cultivar of Dianthus chinensis. These plants like cool weather and usually bloom in the spring in my area of the US - looks like you're living in a region with a mild winter, which means it will be a (possibly short-lived) perennial where you live. The flowers may smell sweetly of cloves.