[WRONG: Please see answers below]
No, it is not thread-safe by default. You shoud use locking-related SQLiteHelper methods to provide thread safety.
[EDIT]: SQLiteDatabase class provides a locking mechanism by default (see comments) and if you are running on multithread, you don’t have to consider changing anything to have thread-safety.
Search for ‘thread’ in this document: http://developer.android.com/reference/android/database/sqlite/SQLiteDatabase.html
And read more on:
- http://www.touchtech.co/blog/android-sqlite-locking/
- Android threading and database locking
- Android — SQLite + SharedPreferences, 2 Threads Simultaneous Read/Write?
- https://groups.google.com/forum/#!topic/android-developers/s3blUf7CRhU