Active Participation
Generally, you are considered to actively participate if you participated in making management decisions or arranging for others to provide services (such as repairs) in a significant and bona fide sense. Management decisions that are relevant in this context include approving new tenants, deciding on rental terms, approving capital or repair expenditures, and other similar decisions. You do not, however, actively participate if at any time during the year your interest (including your spouses interest) in the activity was less than 10% (by value) of all interests in the activity.
For more information see page 2 of IRS Form 4835.