Well it depends on the locking scheme that you are using with the database. On any case the whole table will not lock, however there is always the potentional for that data page you are selecting could be locked and have to wait until your select was finished for a transaction to grab that same data page.
As a good practice it's always a practice to use the WITH (NOLOCK) hint
Example
SELECT * FROM TableName WITH (NOLOCK)
You can also specify the (NOLOCK) hint directly after the TableName