There are two ways in which an object can acquire a negative charge.

1. The negative charges may be transferred to it from another object. By losing negative charges, the second object becomes positively charged (or less negatively charged.)
2. Positive charges could be being transferred to another object in the form of positive ions. The effect is the same for this second object as it was in the first case.

(We are ignoring more exotic effects like pair production in this discussion, but the effect is the same.)