That’s fine. You don’t need to multiply by dt as the value you got from mouse is already the mouse distance (pixels) since last frame.
You only need to multiply by dt for animations that are defined as velocities (pixels/seconds or rotations/seconds). By multiplying by dt (seconds) you cancel out the time and get distances out of velocities ( (pixels/seconds)*seconds = pixels).
To put this into some perspective, the mouse velocity is mouseSpeed = mouseDelta/dt.
Additionally a nice thing you can do is to normalize the mouse input by dividing it by Window.ClientBounds. This will give users a similar feel across different devices and window sizes.