Hi,
it depends on your Oracle version, time which lasted from the transaction COMMIT and/or current database workload.
From 9i, you may use flashback query to retrieve data from given time (in your case it would be before committing the wrong transaction).
From 10g, you may flashback the whole table to that time.
These techniques are described in many articles on web, e.g. here:
http://www.oracle-base.com/articles/...hbackQuery.php
http://www.oracle-base.com/articles/...ashback10g.php
Note, that data obtained will be exactly the same as before that wrong transaction commit; any other changes made from that time will not be reflected in those techniques. So, if you/anybody else made any other changes after that wrong transaction, you will lose them with flashback table. In flashback query, you may be more successful by selecting primary key with wrong column/rows and recovering only them.
If this not possible, the other option would be recovering it from backup (again, only data before that wrong transaction). You should ask your DBA for doing that.