In this paper a class S H 0 (n , q , A , B) of harmonic functions f ∈ H 0 , associated with a q-Ruscheweyh operator is defined. A necessary and sufficient convolution condition for a function f ∈ H 0 to be in this class is proved. A sufficient coefficient condition for the harmonic functions to be in S H 0 (n , q , A , B) and to be sense preserving and univalent is also obtained. It is proved that this coefficient condition is also necessary for the functions in its subclass T S H 0 (n , q , A , B). Using this necessary and sufficient coefficient condition, results based on the convexity and compactness of the class T S H 0 (n , q , A , B) , extreme points for the functions in the class T S H 0 (n , q , A , B) are obtained. Further results on the radii of q -starlikeness of order α , for the functions in the class T S H 0 (n , q , A , B) are obtained. [ABSTRACT FROM AUTHOR]