Looks like you just need to do:
activityImageView.frame = CGRectMake(280, 5, 34, 34);
The first 2 parameters in CGRectMake call above are the X and Y coordinates of the view's top left corner relative to its superview. The remaining parameters are the desired width and height of the view.
Also, don't forget to add your image view to a superview, e.g.
[self.view:addSubview:activityImageView];