Which report you run depends upon what you mean by active. By default all reports in the Reporter are about active, e.g., not terminated, volunteers. So you can run a Volunteer Address list or any of that sort.
One big exception, however, is Statistics and Hours reports, which will include terminated volunteers if they served hours during that period requested.
If you want to see who served hours, but only those who are currently active, aka not terminated, you can make a filter for only those non-terminated people who served hours during a period.
You can use this filter on any hours based report to exclude those who have served hours but are terminated.
If you want a report of hours broken down by individual volunteers, then try the report Hours Served, Summary by Volunteer. Choose the date range last year. Select the Active Served Hours filter.
If you want a compilation of total hours for all your volunteers during the time period you set, the Statistics report Total Enrollment and Hours will give you a compilation of total hours for all you volunteers during the time period you set. Choose Last Year in the date range.