Registration under Service Tax Act is required if the turnover exceeds threshold limit of Rs. 10 Lakh. In case the turnover in an accounting year does not exceeds Rs. 10 Lakh then the concerned person (Service Provider/ Receiver) is not compulsory required to get registered under Service Tax Act.
However, as per Notification No. 26/2005-ST dated 07-06-2005, person providing taxable service in excess of Rs. 9 Lakhs per annum (but les than Rs. 10 Lakhs) will have to register with Superintendent of Central Excise under Service Tax provisions, though they will be eligible for exemption if turnover is less than Rs. 10 Lakhs per annum.