Yes, it's ok. In fact it's going to be pretty widely used when using things like Relational Combo. You're going to have multiple FKs in your table.

Thanks for your answer and I know what you mean by relational combo (small tables for static data) but my table has more meaningful tables with multiple FKs that actually store real data but that data could be related to different parent table (depending on which master table this child table is serving in a particular situation which means that there could be null keys in some of the FKs).
Is it ok for FKs to be null for some records?

That depends on how you have things setup. I have two tables now where basically an Orders Table and a Parts Table(only 1 at a time, otherwise would need a junction table), where basically the order gets quoted, a record is created, and than later if they buy it, we assign a part from the other table which is the FK in the Orders Table, so it has null values all the time. Only thing you really need to be aware of is when making queries with the tables, you need to use outerjoins in some areas to include all the orders (ones without FKs) if you need to work with all of the orders.

Yeah, multiple foreign keys is almost always the norm. Take an Order table for example. You'd have a CustomerID, SalesRepID, ServiceTechID, etc. These are all FKs.